The AMSP (Arzneimittelsicherheit in der Psychiatry) study is a drug safety program that ensures the continuous assessment of severe adverse drug reactions (ADR) in psychiatric inpatients under the natural conditions of routine clinical treatment. It developed out of the preceding drug surveillance study AMÜP (Arzneimittelüberwachung in der Psychiatrie). Currently 35 hospitals participate in the study. This paper describes the methods of the AMSP, gives detailed definitions of ADRs assessed to be ”severe,” and discusses the implications of these definitions and the methodological approach for evaluating the AMSP data. In addition, some overall data compiled on ADR rates from 1993 to 2000 are given.