Priapism is a condition of prolonged penile erection which often causes pain and is unrelated to sexual desire. There is a high risk of impotence despite immediate intervention. The incidence has doubled since the introduction of intracorporeal injection therapy for impotence. Two subtypes of priapism have been described, depending on the underlying cause. The more common type, termed low flow, is characterised by inadequate venous outflow, leading to a hypoxic painful prolonged erection. The etiology is either idiopathic or related to intracorporeal injection therapy. Treatment consists of aspiration and instillation of a diluted alpha-adrenergic agent, or surgery, depending on the degree of hypoxia. The less common subtype, high flow, is arteriogenic, and causes less pain and no ischemia. Injury to a cavernous artery leads to a fistula between the artery and the corpora cavernosa. Treatment is either conservative with immediate ice pack and compression, or delayed selective embolization of the fistula.