This study examined the associations between self-reported attachment style dimensions and romantic relationship functioning over 1 year in a sample of heterosexual dating couples between the ages of 18 and 25 (115 dyads at T1, 57 dyads at T2; 74% Caucasian). Relationship functioning was assessed at multiple levels of analysis via self-reports of interpersonal functioning, observers' ratings of dyadic interactions, and measures of autonomic responding during the interactions. No significant cross-sectional associations were found between attachment style dimensions and interpersonal functioning. However, individuals who reported greater attachment-related anxiety at T1 described their relationships as being of lower quality, were rated by observers as interacting less positively, and exhibited greater electrodermal reactivity during interactions 1 year later.