Background: Interpersonal relationships are substantially codetermined by nonverbal communication, e.g. facial affect. Given the deficits of nonverbal affect recognition and expression in alexithymia, we hypothesized that alexithymics had more interpersonal problems than nonalexithymic individuals, and that the various facets of the alexithymia construct are differentially related to interpersonal problems. Method: 149 subjects participating in an inpatient group psychotherapy program completed the Toronto Alexithymia Scale (TAS-20) and the Inventory of Interpersonal Problems (IIP-C) at the beginning of the treatment. The IIP-C was also administered to a subgroup at the end of the treatment. Results: Based on the alexithymia scores, patients were classified as low- (TAS-20 score ≤51), moderate- or high-alexithymic (TAS-20 score ≧61). High-alexithymic patients had significantly more interpersonal problems than low alexithymics, particularly in the IIP-C scales indicating hostility and social avoidance. The TAS-20 subscale difficulty describing feelings showed the highest correlations with interpersonal problems (r between 0.23 and 0.55). At the end of the treatment, the high alexithymics still scored highest on the IIP-C, but the magnitude of change in interpersonal problems did not differ across the groups. Conclusions: Our findings suggest that the interpersonal style of alexithymic individuals is characterized by a cold and socially avoidant behavior, corresponding to the predominantly insecure attachment pattern found in alexithymia. Additionally, our results indicate that group psychotherapy is as helpful for alexithymic as for nonalexithymic subjects with respect to interpersonal problems. Finally, we propose that alexithymia involves a reduced capacity to use social interactions for affect regulation.