The occurrence and age distribution of patients with adverse drug reactions (ADR) were studied on the basis of a total of 17,653 admissions to the medical divisions of the Zieglerspital Bern and the Anna-Seiler-Haus, Inselspital Bern, during the period 1976-1982. Among this population 12,424 patients (70.4%) happened to have been treated with hypnotics, sedatives or anxiolytics. Results are as follows: 1. The occurrence rate of psychic and neurologic symptoms (with the exception of somnolence and hangover) is 0.14% of all treatments if the casualty category "definitely or probably drug-induced" is considered. For "other ADR" (non-psychic, non-neurologic) the rate is 0.16%. For the benzodiazepine preparations, the psychic and neurologic ADR occurred at about the same rate as for the neuroleptic drugs studied, whereas "other ADR" related to benzodiazepines were observed in only 0.04% of treatments. 2. There is a marked difference in ADR symptoms between benzodiazepines and neuroleptics. With benzodiazepines the most severe reactions were two episodes of shortlived respiratory arrest immediately after intravenous administration. With neuroleptic drugs the most severe symptoms were choreoathetosis, dyskinesia, hyperkinesia and Parkinson's syndrome. There was no fatal reaction. 3. With benzodiazepines there is a slight but significant increase in the occurrence of psychic and neurologic symptoms in the older group of patients, as compared to the younger patients, whereas with neuroleptics there is no age dependence.