This paper illustrates an extension of the APIM technique within a path analysis framework by using cross-informant data on the outcome variable. Data for the current study were derived from a sample of young adult heterosexual couples who had been in a romantic relationship for at least four months (N = 115 couples). The findings from the current study indicate that romantic relationship satisfaction is associated with externalizing behavior problems among both females and males, but that both dyadic data and cross-informant reports are needed to understand this association. Not considering dyadic or cross-informant data may lead to different, and potentially misleading, claims. The findings from the current study provide clear evidence that incorporating cross-informant data in dyadic data analyses provides important new insights into understanding the association between romantic relationship functioning and individual outcomes. (Contains 2 figures and 1 table.)