Aims and objectives To explore the effects of introducing an electronic medication management system on reported medication errors. Background Computerised medication management systems have been found to improve medication safety; however, introducing medication management system into healthcare environments can create unanticipated or new problems and opportunities for medication error. Design Descriptive analysis of medication error reports. Methods This was a retrospective analysis of 359 incident reports drawn from the period of 1 May 2005–30 April 2006 across two hospital sites of a single not-for-profit private health service located in metropolitan Melbourne. Site A used a conventional pen and paper system for medication management, and Site B had introduced a computerised medication management system. Results Most medication errors occurred at the nurse administration (71·5%) and prescribing (16·4%) stages of delivery. The most common medication error type reported at Site A was omission (33%), and at Site B was wrong documentation (24·2%). A higher proportion of errors at the prescribing phase, and less nurse administration errors, were detected at Site B where the medication management system was in use. The incidence of other, less frequent errors was similar across the two hospital sites. Conclusions This examination of medication error reports suggests there are differences in the types of medication errors that are reported in association with the introduction of electronic medication management system compared to pen and paper system systems. The findings provide a new insight into the effects of introducing an electronic medication management system on the types of medication errors reported. Relevance to clinical practice The findings provide a new insight into the types of medication errors that are reported during implementation of an electronic medication management system. Extra support for physicians prescribing practices should be considered.