BACKGROUND: Patients boarded in the emergency department (ED) with psychiatric complaints may be at risk for medication errors. However, no studies exist to characterize the types of errors and risk factors for errors in these patients. OBJECTIVE: To characterize medication errors in psychiatric patients boarded in ED, and to identify risk factors associated with these errors. METHODS: A prospective observational study conducted in a community ED included all patients seen in the ED for primary psychiatric complaints and remained in the ED pending transfer to a psychiatric facility. An investigator recorded all medication errors requiring an intervention by an emergency pharmacist. RESULTS: A total of 288 medication errors in 100 patients were observed. Overall, 65 patients had one or more medication errors. The majority of errors (n = 256, 89%) were due to errors of omission. The final severity classification of the medication errors was: Insignificant (n = 77), significant (n = 152), and serious (n = 3). In the multivariate analysis (R-squared 19.6%), increasing number of home medications (OR 1.17, 95% CI 1.01 to 1.36; p = 0.035), and increasing number of comorbidities (OR 1.89, 95% CI 1.10 to 3.27; p = 0.022) were associated with the occurrence of medication errors. CONCLUSION: Psychiatric patients boarded in the ED commonly have medication errors that require intervention.