The aim of the study is to contribute to knowledge about prescribing-writing errors on prescriptions from hospitals. One hundred and seventy prescriptions, prescribed from Copenhagen University Hospital, were evaluated in a project at Copenhagen University Hospital Pharmacy. Prescriptions were collected at two private pharmacies in Copenhagen during a two-week period in October 1995. The prescriptions contained an average of 1.5 errors and only 11% of the prescriptions were faultless. The three most frequent errors of omission were code of department, inadequate identification of the physician and indications of use. It is often difficult to reach the physician at the hospital, but the first step is to ease the identification of physician and ward. This project confirms that indication of use is a frequent error of omission.