Married people show better health and lower mortality risk than the unmarried (Waite & Gallagher, 2000), but the benefits depend on the quality of the relationship, with poor quality relationships no better and perhaps worse than no relationship (Umberson, Williams, Powers, Liu, & Needham, 2006; Williams, 2003). Marital quality is important across the life span but seems to be particularly important in later life as health tends to decline and the effects of adversity accumulate (Carstensen, 1992; Henry, Berg, Smith, & Florsheim, 2007; Umberson et al., 2006). Marital adversity has been found to accelerate the decline in physical and mental health with age and to increase the risk of dying (Birditt & Antonucci, 2008; Coyne et al., 2001; Hibbard & Pope, 1993; Waite, Luo, & Lewin, 2009). At the same time, poor health can act as a stressor in the marriage, leading to declines in marital quality (Booth & Johnson, 1994; Wickrama, Lorenz, Conger, & Elder, 1997). Most of the research examining the link between physical health and marital quality has investigated how negative interactions in marriage lead to declines in physical health (Choi & Marks, 2008; Kiecolt-Glaser & Newton, 2001; Uchino, Cacioppo, & Kiecolt-Glaser, 1996), with larger effects at older ages (Umberson et al., 2006). Conversely, high-quality marriages can help individuals to cope with stressors and thereby maintain good physical health (Ditzen, Hoppmann, & Klumb, 2008; Warner & Kelley-Moore, 2012). However, the causal mechanisms connecting martial quality and physical health operate in both directions. Indeed, among adults age less than 55, decrements in health have been associated with deterioration in marital happiness (Booth & Johnson, 1994; Wickrama et al., 1997). Furthermore, although decrements in one’s own health have been linked to modest decrements in marital quality, decrements in one’s partner’s health have been linked to quite substantial declines in marital quality (Yorgason, Booth, & Johnson, 2008). This process may be particularly important in later life, when chronic illness becomes common (Yang, 2008). The pathways linking poor health with marital quality in later life have been little examined at the population level, despite the importance of martial quality to individuals and society. In this study, we examine one set of hypothesized pathways. We argue that reduced engagement in sex with one’s spouse, an enriching marital role, is associated with worse marital relationship quality among those whose own health is poor and those whose spouse has physical health problems. Also, marital relationship quality is worse among those with the psychological distress that often accompanies poor physical health in either spouse (Blazer, 2009; Bruce, 2000; Hagedoorn et al., 2001). We develop a conceptual model that links physical health, couple sexual activity, psychological well-being, and marital quality. In our model, ongoing sexual activity mediates the association between physical health and marital quality, as does psychological well-being. We conceptualize sexuality activity and psychological well-being as mediators because especially at older ages the biggest challenges to health come from chronic conditions, which develop slowly over years. In contrast, poor mental health as reflected, for example, in depression, may alter relatively quickly in response to the current situation (Hughes & Waite, 2009; Luo, Hawkley, Waite, & Caccioppo, 2012) as can sexual behavior (Carpenter, Nathanson, & Kim, 2009). Note that although we use the term marital quality for convenience, our analysis includes cohabitors as well. We test a series of hypotheses based on this model using data on both members of older adults in marital and cohabitational dyads from the second wave of the nationally representative National Social Life, Health and Aging Study. Couple Sexual Activity As a Mediator of the Physical Health–Marital Quality Association Poor physical health may be associated with marital quality indirectly through spousal engagement in marital roles. Poor physical health of one or one’s partner may affect the roles partners take in a relationship and the interaction between them in these roles. Hence, in this framework, poor physical health affects marital happiness through poor role performance and less positive (or more negative) interactions. Sexual Behavior Health problems have been linked to problems carrying out social and family roles (Northouse, Mood, Templin, Mellon, & George, 2000). In particular, the health problems of one or one’s partner can interfere with either partner’s desire for or ability to engage in sexual relations (DeLamater & Moorman, 2007; Karraker, DeLamater, & Schwartz, 2011; Laumann, Das, & Waite, 2008). It is important to note that the physical health problems of men may be especially important regarding sexual relations (Lindau et al., 2007). Physical health has been shown to affect satisfaction with sex in a middle-aged population (Carpenter et al., 2009). The link between health problems and sexual activity may help explain the observed association between increased age and decreased engagement in partnered sexual activity (Call, Sprecher, & Schwartz, 1995; Donnelly, 1993), which has been associated with low marital satisfaction (Call et al., 1995; DeLamater & Moorman, 2007; Donnelly, 1993). We hypothesize that marital quality is lower among those with less engagement in partnered sex. Physical Health, Psychological Health, and Marital Quality The impact of poor physical health on psychological distress has been well documented among individuals and in relationships. At the individual level, poor physical health, as indicated by morbidity and frailty, increases the risk for poor psychological health (Blazer, 2009; Bruce, 2000; Ormel, Rijsdijk, Sullivan, van Sonderen, & Kempen, 2002). At the relationship level, one’s partner’s poor physical health, and his or her associated poor psychological health, predicts poor psychological health in the physically healthy partner (Hagedoorn et al., 2001). According to the stress generation model, individuals experiencing psychological distress cause stressful interactions with spouses, which leads to poor marital quality (Davila, Bradbury, Cohan, & Tochluk, 1997; Hammen, 1991). Thus, in this framework, poor physical health leads to stress, which increases the risk of poor psychological health, which in turn increases chances of negative interactions and ultimately poor marital quality. Evidence for this theory has been found among older adults at both the individual and relationship levels. Psychological distress has been shown to mediate the association between one’s own and one’s spouse’s poor health and low marital happiness (Yorgason et al., 2008). Psychologically distressed people have also been shown to have more negative spousal interactions (Kramer, 1993; Rehman, Gollan, & Mortimer, 2008). Though the association between psychological ill health and marital distress is found across the life span (Gierveld, van Groenou, Hoogendoorn, & Smit, 2009; Hawkins & Booth, 2005; Horwitz, White, & Howell-White, 1996; Ross, 1995), it seems to be stronger in older adults (Whisman, 2007). Thus, we hypothesize that psychological health—one’s own and one’s partner’s—mediates the association between physical health—one’s own and one’s partner’s—and marital quality. Dimensions of marital quality. Marital quality consists of both positive and negative dimensions, which are distinct constructs, not merely opposite poles of a single dimension (Fincham, Beach, & Kemp-Fincham, 1997; Fincham & Linfield, 1997). Most research to date has focused mainly on the positive dimension, and on the physical and psychological health correlates of sexual engagement (Carpenter et al., 2009) or, separately, of marital quality. For this reason, we know little about how physical health, psychological well-being, and the sexual engagement of the couple operate together to predict both positive and negative marital quality in a population sample. Conceptual Framework Our conceptual model of the associations among physical health, partnered sexual behavior, psychological health, and marital quality is shown in Figure 1. In this model, poor physical health—either one’s own or one’s partner’s—is linked to lower levels of both one’s own and one’s partner’s psychological health and greater likelihood of low levels of partnered sex. In turn, infrequent partnered sex and poor psychological health are both associated with poor marital quality. Note that this model reflects one set of hypothesized relationships. We discuss alternative models later in the article. We test the following hypotheses: Figure 1. Conceptual model of the associations among physical health, sexual activity, psychological health, and marital quality. 1. We hypothesize frequency of sex with one’s spouse mediates the association between physical health—one’s own and one’s partner’s—and marital quality. 2. We hypothesize that psychological health—one’s own and one’s partner’s—mediates the association between physical health—one’s own and one’s partner’s—and marital quality.