An estimated 50,000 children with autism spectrum disorder (ASD) will turn 18 this year alone (Shattuck, Narendorf, et al., 2012; Shattuck, Roux, Hudson, Taylor, et al., 2012), and the number of adults with ASD will increase rapidly in the coming years (Gerhardt & Lainer, 2011; Shattuck, Narendorf, et al., 2012). However, poor outcomes in terms of education, employment, and the development of social relationships are quite common for this group (Levy & Perry, 2011; Seltzer, Shattuck, Abbeduto, & Greenberg, 2004; Shattuck, Narendorf, et al., 2012), and there is little understanding of discrete reasons for these poor outcomes. The impact of poor outcomes for adults with ASD over the life course combines with the growing population of individuals with ASD (Centers for Disease Control and Prevention, 2012; Shattuck, Roux, Hudson, Taylor, et al., 2012) to make it imperative to understand the behavioral underpinnings of poor adult outcomes. Effectively addressing the substantial and varied needs of the growing number of adults with ASD is thus one of the greatest challenges currently faced by both service providers and the ASD research community. Despite work that has examined the myriad of challenges and problems faced by children with ASD and has led to the development of an array of effective treatments that have helped children with ASD substantially (Cohen, 1980; Odom, Boyd, Hall, & Hume, 2010; Odom, Collet-Klingenberg, Rogers, & Hatton, 2010; Ruble, Heflinger, Renfrew, & Saunders, 2005), there remains a paucity of research that focuses on the specific needs of adults with ASD (Bishop-Fitzpatrick, Minshew, & Eack, 2013; Gerhardt & Lainer, 2011; Levy & Perry, 2011; Shattuck, Roux, Hudson, Taylor, et al., 2012). Most notably, we know very little about why between 50% and 75% of adults with ASD, including those who are more cognitively able, function poorly in terms of achieving some form of formal education, maintaining employment, living independently, and sustaining social relationships (Eaves & Ho, 1996; Howlin, Goode, Hutton, & Rutter, 2004; Levy & Perry, 2011; Shattuck, Narendorf, et al., 2012). We know even less about how to improve these outcomes through some combination of treatments and services designed to target the specific needs of this population. Adults with ASD face many substantial challenges accomplishing basic tasks associated with daily living (Shattuck, Roux, Hudson, Lounds Taylor, et al., 2012; Smith, Maenner, & Seltzer, 2012; Taylor & Seltzer, 2011) which are further exacerbated by their broad and pervasive difficulties with social interactions (Gillespie-Lynch et al., 2012; Klin et al., 2007; Wing & Gould, 1979). These challenges, coupled with biobehavioral vulnerabilities inherent to ASD (Klin et al., 2007; Stanfield et al., 2008; Wing & Gould, 1979), put people with these conditions at increased risk for psychosocial distress (Corbett, Mendoza, Abdullah, Wegelin, & Levine, 2006; Corbett, Mendoza, Wegelin, Carmean, & Levine, 2008; Corbett, Schupp, Levine, & Mendoza, 2009; Jansen, Gispen-de Wied, van der Gaag, & van Engeland, 2003; Lanni, Schupp, Simon, & Corbett, 2012; Levine et al., 2011; Spratt et al., 2011). Stress, and more specifically the way that one responds to and copes with stress, is essential to adjustment in adulthood (Cohen, Kamarck, & Mermelstein, 1983; Cohen & Williamson, 1988; Selye, 1956; Williams, 2008) and likely factors heavily into both daily life and long-term outcomes for adults with ASD, as suggested by a growing literature on stress in children with ASD that indicates that children with ASD have differential biobehavioral responses to physiological arousal than children without an ASD diagnosis (Corbett et al., 2006; Corbett et al., 2008; Corbett et al., 2009; Lanni et al., 2012; Levine et al., 2011; Spratt et al., 2011). In order to design interventions that might help adults with ASD better manage stress and, as a result, function better in adulthood, we must first understand how adults with ASD perceive and respond to stress and how stress factors into adult outcomes for individuals with ASD. A small but growing area of research describes the biological bases behind physiological arousal to stress in children with ASD. Specifically, two recent studies (Levine et al., 2011; Spratt et al., 2011) have examined the relationship between cortisol levels and stress in children with ASD. Levine and colleagues (2011) found that children with high functioning autism are more likely than non-affected children to have a decrease in salivary cortisol levels following a social stress simulation, representing decreased levels of stress in contrast to control participants. Spratt and colleagues (2011) found that a sample of children with ASD had significantly higher peak cortisol levels, a prolonged duration of peak cortisol levels, and a slower recovery from cortisol elevation than a sample of non-affected children. These results are mixed yet suggest that children with ASD may have different reactivity to stress and novel stimuli compared with non-affected children and may indicate a mechanism by which children with ASD are differentially able to adapt to novel social situations. The literature on stress and coping in individuals with ASD indicates that children with ASD respond differently to stress than children without ASD and that children with ASD may have either more or less extreme psychophysiological reactions to stress. While the literature on stress in individuals with ASD focuses solely on children (Levine et al., 2011; Spratt et al., 2011), it is likely that adults with ASD also experience differential psychosocial distress and biological stress in social situations. However, no research indicates whether or not this is the case, and no research associates stress response with social functioning. This paper seeks to address this gap in the literature by examining the relationship between both perceived- and interviewer-observed stress and social functioning in adults with ASD, compared to healthy volunteers. We hypothesized that adults with ASD would experience more perceived and interviewer-observed stress than healthy volunteers. Additionally, we hypothesized that there would be an inverse relationship between stress and social functioning such that higher perceived- and interview-observed stress predicts poorer social functioning in adults with ASD.