Only 13% of adverse drug reactions that should have been reported to the Committee on Side Effects in Sweden according to the criteria published by the National Board of Health and Welfare, were actually reported by the responsible doctors. This was found in a prospective study of all adverse reactions established in 1 271 patients at a department of infectious diseases. It was also found in retrospect that only half of the patients affected by complications making them eligible for compensation from the Patients' Insurance Office existing in Sweden actually received compensation, while the Drug Insurance Office was better utilized. Various reasons for these low reporting frequencies are discussed.