Comorbid mental disorders of DSM-IV axis I and axis II have repeatedly been found to be a negative predictor for the treatment of axis I disorders, although recent contrary findings exist. Little is known about the effect of comorbidity on the therapy outcome of somatoform disorders. We compared three types of comorbidity, (1) personality disorders (PDs), (2) major depression (MDD) and anxiety (ANX) disorders, and (3) PDS and MDD and ANX, with regard to their relevance for the treatment outcome of somatoform disorders. One hundred twenty-six inpatients were assessed at least 4 weeks before admission to treatment, upon admission, and again at discharge. Somatoform, hypochondriacal, and depressive symptomatology, dysfunctional cognitions about body and health, dysfunctional social relationships, and other clinical characteristics were measured. Diagnostic assessments were based on the DSM-IV, Our findings suggest that none of the three types of comorbidity influence the therapy outcome of somatoform disorders or have a modifying effect on the level of psychopathology, Copyright (C) 1999 by W.B. Saunders Company.