Low doses of megestrol acetate are frequently used for treatment of hot flashes in men having androgen ablation for prostate cancer. We report a case in which megestrol acetate (20 mg bid) was administered for symptomatic control of hot flashes in a medically castrated patient with prostate cancer. The patient was subsequently noted to have a rising prostate-specific antigen (PSA) level. Megestrol acetate administration was discontinued, and the PSA level declined. These data indicate that even the low doses of megestrol acetate used for control of hot flashes can be associated with PSA increases in some patients with prostate cancer.