Prolonged pharmacological erection (PPE) is a blocked erection lasting for more than 4 hours after intracavernosal injection (ICI) of an erectogenic drug. This form of priapism is the commonest complication of ICI in the diagnosis and treatment of impotence. It carries a potential risk of acute ischaemia of the corpora cavernosa with subsequent destruction of the erectile tissues. Any blocked erection must therefore be treated within 4 hours. Medical treatment is sufficient in the very great majority of cases, provided it is performed early. The indication for each medical method (simple measures, oral or, more especially, intracavernosal alpha-stimulant treatment, decompressive cavernosal puncture) depends on the duration of PPE and/or the presence of signs of tissue ischaemia (pain). Surgery is only indicated in the rare cases of failure of medical treatment. PPE can now be prevented by means of selection and information of patients and the recent introduction of less dangerous drugs.