Objectives: Medication reconciliation is the process of comparing a patient's hospital medication orders to all of the medications that the patient has been taking prior to admission. The primary aim of this study was to evaluate the effectiveness of pharmacist-led medication reconciliation in reducing ED visit rates. The secondary aim of this study was to evaluate if a clinical pharmacist reduces medication errors in an ED observation unit (OBS). Methods: This was a retrospective, IRB approved, chart review conducted at New York University Langone Health-Tisch Hospital. The study defines the year before a clinical pharmacist was present on the unit (July 5, 2016 through July 4, 2017) as the control group and the first year a clinical pharmacist was present on the unit (July 5, 2017 through July 4, 2018) as the intervention group. The primary endpoint was 30-day ED re-visits. The secondary endpoints were 60-and 90-day ED re-visits, number, type and severity of medication history and reconciliation discrepancies. Results: The primary endpoint of 30-day ED visits occurred in 153 patients in the no pharmacist group and 88 patients in the OBS clinical pharmacist group (19.1% vs 9.9%, P < .00001). The secondary endpoint of 60- day ED visits occurred in 53 patients in the no pharmacist group and 39 patients in the OBS clinical pharmacist group (8.2% vs 4.9%, P = .01). The secondary endpoint of 90- day ED visits occurred in 31 patients in the no pharmacist group and 26 patients in the OBS clinical pharmacist group (5.2% vs 3.4%, P = .01). Conclusion: The benefits of having a clinical pharmacist perform medication reconciliation are highlighted by the reduction in ED visits, cost savings, and the prolific amount of errors corrected.