A device implanted in the penis that assists it to become erect. The device is used in patients with erectile dysfunction due to such organic causes as trauma, prostatectomy, or diabetes. It is usually in the form of inflatable plastic cylinders implanted in each corpus cavernosum of the penis. These cylinders are attached to a pump embedded in the scrotal pouch. A reservoir for the fluid used to fill the cylinders is implanted behind the rectus muscle. This system allows the cylinders to be filled when an erection is desired and the fluid to be drained back into the reservoir when the need for the erection has passed. In most patients, this device permits the attaining of a nearly physiological erection.