Drug administration is an integral part of the nurse's role. Responsibility for correct administration of medication rests with the nurse, yet medication errors are a persistent problem associated with nursing practice. This review examines what constitutes a medication error and documents contributory factors in medication errors. These factors have been derived from reported medication errors and opinions of nurses as to factors which predispose to errors. A number of definitions exist as to what constitutes a medication error. The definition used should facilitate interpretation and comparison of a wide range of research reports. Medication errors are a multidisciplinary problem and a multidisciplinary approach is required in order to reduce the incidence of errors.