Between 2002 and 2004 485 cancer patients in oncological treatment were assessed for mental disorders using the Structured Clinical Interview for DSM-IV (SCID). Socio-demographic, psychosocial and medical data were taken as possible predictors into multivariate analysis. 32 % of the patients suffered from mental diseases. Significant risk factors for anxiety disorders were female sex, precedent mental trauma, children below 18 years; for affective disorders female sex, poor physical functioning; for stress disorders children below 18 years; for addictive disorders male sex, younger age, children from 18 years on, distant metastases. Additional psychosocial risk factors seem to be predominantly responsible for the development of a mental co-morbidity in inpatients with malignant diseases, which should be examined in doctor-patient-talks.