Several investigators have recently developed guidelines for determining which patients with tricyclic antidepressant overdose should be hospitalized. The width of the QRS complex on the ECG and several clinical parameters have been proposed to identify patients at risk for major complications. To validate these, we developed an algorithm and then applied it to 45 patients who had overdosed on tricyclic antidepressants. This algorithm correctly predicted which patients required admission, whether due to present or impending complications, and which patients could have been discharged without morbidity or mortality. We conclude that use of the modified algorithm can identify patients with tricyclic antidepressant overdose who can be safely discharged from the emergency department.