A 29-year-old man experienced four episodes of prolonged painful erection while being treated with perphenazine for paranoid schizophrenia. Each episode of priapism lasted five hours or longer. On two occasions, aspiration of blood from the corpora cavernosa resulted in detumescence; the other episodes were successfully managed with operative shunting of blood from the congested cavernosa. Perphenazine was discontinued after the fourth episode of priapism and antipsychotic treatment with thiothixene was subsequently initiated. During 16 months of follow-up, the patient has reported normal erections without repeat episodes of priapism.