Several studies indicate that the public does not differentiate between professional activities provided by psychotherapists, psychiatrists and psychologists. 543 psychiatric outpatients completed a questionnaire concerning mental health professionals' competence. Patients were least familiar with the competence "psychological testing". 35 % respectively 40 % of our patients expected that psychologists or psychotherapists could prescribe psychopharmacological drugs. 47 % expected counsellors to provide psychotherapy, 44 % expected diagnostic competence. Physicians' diagnostic and psychopharmacological competence was underestimated. Mental health professionals should not trust in patients' knowledge concerning their professional activities. Especially in the beginning of a diagnostic or therapeutic process patient information is of major importance.