This study aimed to explore the associations among attachment system type, sexual satisfaction, and marital satisfaction in adult couples in stable relationships. Participants were 294 couples between the ages of 20 and 70 years who answered self-administered questionnaires. Hierarchical linear modeling revealed that the anxiety and avoidance, sexual satisfaction, and marital satisfaction dimensions were closely related. Specifically, the avoidance dimension, but not the anxiety dimension, corresponded to lower levels of sexual and marital satisfaction. Moreover, for the sexual satisfaction variable, an interaction effect was observed between the gender of the actor and avoidance of the partner, which was observed only in men. In the marital satisfaction dimension, effects were apparent only at the individual level; a positive relation was found between the number of years spent living together and greater contentment with the relationship. These results confirm the hypothetical association between attachment and sexual and marital satisfaction and demonstrate the relevance of methodologies when the unit of analysis is the couple.