There is increasing evidence that attitudes and beliefs are important in predicting adherence to treatment and medication in depressive and bipolar disorders. However, these attitudes have received little study in patients whose disorders were sufficiently severe to require hospitalization. The Antidepressant Compliance Questionnaire (ADCQ) was mailed to a large population of patients with depressive or bipolar disorder, representative of patients treated in hospital settings in Denmark. Of the 1005 recipients, 49.9% responded to the letter. A large proportion of the patients (40-80%) had erroneous views as to the effect of antidepressants. Older patients (over 40 years of age) consistently had a more negative view of the doctor-patient relationship, more erroneous ideas concerning the effect of antidepressants and a more negative view of antidepressants in general. Moreover, their partners agreed on these negative views. Women had a more negative view of the doctor-patient relationship than men, and patients with a depressive disorder had a more negative view of antidepressants than patients with bipolar disorder. The number of psychiatric hospitalizations or the type of treating physician (general practitioner, psychiatrist in private practice, community psychiatrist, hospital psychiatrist, other doctor) did not affect attitudes and beliefs. Lack of knowledge about affective disorder and its treatment and a critical attitude, especially among older patients, may add to an adverse prognosis of depressive and bipolar disorders.