The present study was designed to investigate links between dimensions of romantic attachment and relationship functioning in a cross-sectional sample of people in same-sex relationships, with the goals of replicating basic findings from research on heterosexual couples and advancing understanding of unique issues faced by same-sex couples. The sample included 274 female couples, 188 male couples, 34 women whose female partners did not participate, and 39 men whose male partners did not participate. Participants were recruited from geographically diverse regions of the United States and Canada and provided data by responding to pencil-and-paper surveys. Attachment insecurity in both self and partner were linked with poor relationship functioning across a range of variables (satisfaction, commitment, trust, communication, problem intensity). The pattern of results was identical for women and men, but the effects were stronger in male couples for some associations between attachment variables and indices of positive relationship functioning. Monogamy was positively associated with relationship quality only when participants or their partners reported moderate or high levels of attachment anxiety. Contrary to hypothesis, attachment did not moderate links between minority stressors and relationship functioning. (Contains 3 tables.)