Decision making in psychiatric diagnosis and treatment has not been evaluated systematically. The authors present a model for treatment of an acute manic episode using a decision analysis software program. Six treatment options were put into the model: lithium, valproate, carbamezepine, electroconvulsive therapy, clonazepam, and neuroleptics. Each treatment was evaluated on three factors, efficacy, tolerability, and cost, using data from the literature and pharmacy and billing information. Output from the computer program identified three top choices among the six options: valproate, carbamazepine, and lithium, with valproate emerging as the first choice using the data we inputted.