Background. Cognitive therapy reduces depressive symptoms of major depressive disorder, but little is known about concomitant reduction in social-interpersonal dysfunction.

Method. We evaluated social-interpersonal functioning (self-reported social adjustment, interpersonal problems and dyadic adjustment) and depressive symptoms (two self-report and two clinician scales) in adult outpatients (n=156) with recurrent major depressive disorder at several points during a 20-session course of acute phase cognitive therapy. Consenting acute phase responders (n=84) entered a 2-year follow-up phase, which included an 8-month experimental trial comparing continuation phase cognitive therapy to assessment-only control.

Results. Social-interpersonal functioning improved after acute phase cognitive therapy (dyadic adjustment d=0·47; interpersonal problems d=0·91; social adjustment d=1·19), but less so than depressive symptoms (d=1·55). Improvement in depressive symptoms and social-interpersonal functioning were moderately to highly correlated (r=0·39–0·72). Improvement in depressive symptoms was partly independent of social-interpersonal functioning (r=0·55–0·81), but improvement in social-interpersonal functioning independent of change in depressive symptoms was not significant (r=0·01–0·06). In acute phase responders, continuation phase therapy did not further enhance social-interpersonal functioning, but improvements in social-interpersonal functioning were maintained through the follow-up.

Conclusions. Social-interpersonal functioning is improved after acute phase cognitive therapy and maintained in responders over 2 years. Improvement in social-interpersonal functioning is largely accounted for by decreases in depressive symptoms.