Half a century of theoretical accounts, case histories, and evidence implies perfectionism limits the success of psychotherapy and makes it hard for people to participate in and benefit from close relationships. Likewise, intimate relationships are crucial determinants of the success of treatment. However, the extent to which specific types of relationships explain why perfectionism leads to a poorer treatment outcome is unclear. We addressed this by, first, testing whether the perfectionism traits of self-oriented, other-oriented, and socially prescribed perfectionism hindered symptom reduction in group psychotherapy for depression and, second, assessing the mediating role of romantic love, friendships, and familial love on the effects of perfectionism traits on change in depression. Psychiatric patients (N = 156) enrolled in short-term postdischarge group cognitive-behavioral therapy for residual depression completed measures of perfectionism at pretreatment; of romantic love, friendships, and familial love at posttreatment; and of depression at pre- and posttreatment. Multilevel modeling showed that other-oriented and socially prescribed perfectionism were associated with lower posttreatment reductions in depression over treatment, and path analysis revealed that self-oriented, other-oriented, and socially prescribed perfectionism indirectly predicted lower posttreatment reductions in depression through a perceived lack of quality friendships. Results lend credence and coherence to the perfectionism social disconnection model in a clinical context and underscore the importance of taking extratherapeutic social disconnection into account when treating perfectionistic patients. (PsycInfo Database Record (c) 2020 APA, all rights reserved).