Aim: Based on a multidisciplinary review of drug use in nursing home residents, this study aimed to identify the most frequent clinically relevant medication problems and to analyse them according to the drugs involved and types of problems. Methods: Cross sectional study auditing drug use by 1354 residents in 23 nursing homes in Bergen, Norway. Data were collected in 1997. A physician/pharmacist panel performed a comprehensive medication review with regard to indications for drug use and active medical conditions. The drug related problems were subsequently classified according to the drugs involved and types of problems (indication, effectiveness, and safety issues). Results: 2445 potential medication problems were identified in 1036 (76%) residents. Psychoactive drugs accounted for 38% of all problems; antipsychotics were the class most often involved. Multiple psychoactive drug use was considered particularly problematic. Potential medication problems were most frequently classified as risk of adverse drug reactions (26%), inappropriate drug choice for indication (20%), and underuse of beneficial treatment (13%).