The penis consists of basically three cylinders, covered by several sheaths of tissue and, finally, by skin. Running the length of each side of the penis are spongy cylindrical structures called the corpora cavernosa. These form the erectile tissue that becomes engorged with blood during erection, acting like the inner tube of a tyre. They are surrounded by the tunica albuginea, a tough, inelastic, fibrous sheath, which might be compared with the tyre itself. When the penis becomes erect, the inner tubes (corpora cavernosa) inflate, filling the space within the tyre (tunica albuginea), making it more rigid.

In Peyronie's disease, tough, fibrous plaques spontaneously appear within the tunica albuginea, and are felt as tender lumps. When the penis becomes erect, it inflates unevenly and tends to bend around the plaque, causing the characteristic deformed appearance of Peyronie's disease.

Experts are not certain why some men get Peyronie's disease and others do not. Several factors might be involved, including:

• genetics: occasionally the disease has a tendency to run in certain families (inherited or genetic predisposition), but this is not common.
• injury: Peyronie's disease is more common after injury to the penis, such as penile fracture or forceful bending of the erect penis. It also occurs more frequently in men that give injections into the penis for the treatment of erectile dysfunction (impotence).
• circulatory disorders: more men with Peyronie's disease seem to be affected by high blood pressure and hardening of the arteries (atherosclerosis), so these conditions might possibly be involved in its development.
• diabetes: this is more common in men with Peyronie's disease. As a result diabetes might also be involved in its development Peyronie's disease is more common after injury to the penis, such as penile fracture or forceful bending of the erect penis. It also occurs more frequently in men that give injections into the penis for the treatment of erectile dysfunction (impotence).