Rationale, aim and objectives: Medication error is common and the most common form of administration error is omission. Implementation of Electronic Medication Management systems (eMMS) has been hypothesized to decrease the rate of omitted doses due to the creation of a number of forcing functions and decision support tools however there is limited evidence currently available in the literature to support this assumption. This study therefore aims to ascertain if implementation of eMMS at 2 acute metropolitan hospitals reduces the rate of omitted doses Method: A retrospective cohort study was undertaken pre and post implementation of eMMS. Patients meeting eligibility criteria had all medication charts from their admission reviewed and an omitted dose rate calculated. For each omitted dose identified; medication name, imprest availability, dispensing history, administration time and frequency were recorded. Results: 386 patients met eligibility criteria for this study (11,796 opportunities for omission). The implementation of eMMS was associated with a significant reduction in omitted doses (3.6% vs 1.8% p<0.01). Benefit was not consistent among subgroups. eMMS implementation at the hospital with the higher baseline omitted dose rate was associated with a significant reduction in omitted doses (5.8% vs 0.9% p<0.01) but not at the hospital with a lower baseline rate (2.7% vs 2.4% p=0.3). The most common times for an omitted dose to occur were 0800 (33%) and 2000 (18%). The most common frequencies for an omitted dose were daily (35%) and twice daily (32%). Conclusion: The introduction of eMMS was associated with a decrease rate of omitted doses. Greatest benefit is likely to occur in areas with a high baseline rate of omission.