To determine the frequency and clinical significance of medication errors when (a) pharmacists elicit medication histories in the Emergency Department after medications have been prescribed by doctors and (b) pharmacists obtain and chart medication histories prior to doctors' approval. The Queen Elizabeth Hospital, a 350 bed South Australian teaching hospital, serving the local adult community. Emergency Department patients at risk of medication misadventure were recruited in two phases with a 'usual practice' arm (6 weeks) and a 'pharmacist medication charting' arm (5 weeks) reflecting an alternative intervention. In the 'usual care' arm, medication histories were compiled by a pharmacy researcher after a doctor had completed the medication chart. The researcher-elicited medication histories were compared with the doctors' medication charts and unintentional discrepancies were recorded. In the 'pharmacist medication charting' arm, the same process was followed except the researcher compiled the patients' medication histories at triage, prior to patients seeing a doctor. The medication history was then transcribed onto a medication chart for authorisation by a doctor. In addition, whether resolution of unintentional discrepancies for patients in the 'usual care' arm had occurred by discharge was determined by examining patients' medical records. Main outcome measure Frequency of unintentional discrepancies and medication errors. The study included 45 and 29 patients in the 'usual care' and intervention arms, respectively. In the 'usual care' arm, 75.6% of patients had one or more unintentional discrepancies compared with 3.3% in the 'pharmacist medication charting' arm. This resulted in an average of 2.35 missed doses per patient in the 'usual care' arm and 0.24 in the intervention arm. In addition, an average of 1.04 incorrect doses per patient were administered in the 'usual care' arm and none in the 'pharmacist medication charting' arm. The differences observed between the arms were statistically significant (P < 0.05) and deemed clinically significant by a multidisciplinary panel. This study provides evidence for pharmacists eliciting medication histories to prepare medication charts at the earliest possible opportunity following a patient's presentation to the Emergency Department.