INTRODUCTIONMany studies have found that ethnic heterogamy, or exogamy, is associated with increased dissolution risks of marriages and cohabiting unions (Jones, 1996; Finnas, 1997; Kalmijn et al., 2005; Dribe and Lundh, 2012; Saarela and Finnas, 2014). As compared with ethnically homogamous unions, partners of ethnically mixed unions can be assumed to have more divergent cultural norms, values and tastes, which will make it more difficult to make joint decisions about the future, including plans about marriage, childbearing, and upbringing (Kalmijn, 1998). In that perspective, the relatively high dissolution risk of ethnically mixed couples comes as no surprise.The traditional approach has been to use information about the ethnic affiliation of each partner in the couple, as generally recorded in population censuses of different countries. In unions with children, additional insights into the relation between ethnic heterogamy and union stability can be gained by infomation about how the offspring is ethnically categorised. To our knowledge, this approach has not been fully utilised in previous research. In this paper, we demonstrate how it can be accomplished using data from Finland.The decisions made after union formation may be more thoughtful than behaviours before mating. If parents of ethnically mixed unions are forced to make a decision about the ethnic categorisation of their children, a conscious choice must be made and this choice might reflect some agreement based on the parents' ethnic preferences (see Xie and Goyette, 1997; Qian, 2004). Ethnic awareness is then reflected by how the ethnically mixed couples choose their children's ethnic affiliation. This is particularly the case in Finland, since the parents must choose how a new-bom baby is ethno-linguistically classified at the time when it enters the country's electronic population register, and this generally occurs when the child is baptised. In contrast to classical assimilation theory, which considers intermarriage to be the final stage of a minority group's assimilation into mainstream society (Gordon, 1964), ethnic awareness may instead be heightened just because of the contrast and competition with the norms of mainstream society and the direct contact with the majority group (Olzak, 1983; Saenz et al., 1995). Ethnic identification of children from interethnic marriages provides an opportunity to exercise one's options (Hout and Goldstein, 1994), and actual behaviour rather than attitudes serves as a guide to individuals' orientation towards their own and other ethnic groups (Finnas and O'Leary, 2003).In this study, we focus on the stability of ethnically mixed and homogamous unions in Finland, and argue that the first-bom child's ethnic affiliation can be used as a rough indicator of individual preferences towards ethnically related norms, values and tastes. Using detailed longitudinal data from population registers, which contain a single classification of each person's ethno-linguistic group, we demonstrate how information about the children can be used to enhance our understanding of previous research on union stability. Since these electronic registers cover the entire population of the country, access to representative samples are easily obtained. The primary aim is to analyse whether it is possible to find effects of ethnic-related individual preferences in terms of how parents in ethnically mixed unions have chosen to register the child. In spite that the prerequisites for this kind of detailed analysis are unusual in an international perspective, we are confident that the behaviour studied here is not unique to this one society, but should be applicable to many other ethnic or religious groups as well (see e.g., Chew et al., 1989; Judd, 1990; Xie and Goyette, 1997; Qian, 2004; Finnas and O'Leary, 2003; Lee and Edmonston, 2005). The particular case of Finland is described next.CONTEXTApproximately 90 per cent of the population in Finland consists of native Finnish speakers, while there also is an indigenous ethno-linguistic group of Swedish speakers that amounts to 291,000 persons, or 5. …