Peyronie's disease is characterized by a plaque, or hard lump, that forms on the penis. It may develop on the upper or lower side of the penis in layers containing erectile tissue. The penis contains balloon-like blood vessels that fill with blood to cause an erection. Scar tissue forming in the balloons cannot stretch as much as the balloons do, so the erected penis bends toward the side with a scar. The plaque often begins as a localized inflammation that may develop into a hardened scar. Generally, when the disease heals within a year or so, the plaque does not advance beyond that initial inflammatory phase. When the disease lasts for years, the plaque often becomes a tough fibrous tissue, and calcium deposits may form.

Most experts believe that Peyronie's disease is likely the consequence of a minor penile trauma. The most common source of this type of penile trauma is thought to be vigorous sexual activity (e.g., bending of the penis during penetration, pressure from a partner's pubic bone, etc.) although injuries from sports or accidents may also play a role. Injury to the tunica albuginea may trigger a cascade of inflammatory and cellular events resulting in a process called fibrosis, a medical term for formation of excessive scar tissue. This abnormal scar tissue in turn forms the plaque of Peyronie's disease.

Not all men who suffer occasional mild trauma to the penis develop Peyronie's disease. For this reason, most researchers believe that there must be genetic or environmental factors that contribute to the formation of Peyronie's disease plaques. Men with certain connective tissue disorders (such as Dupuytren's contractures or tympanosclerosis) and men who have a close relative with Peyronie's disease have a greater risk of developing the condition. Certain health conditions such as diabetes, tobacco use, or a history of pelvic trauma may also lead to abnormal wound healing and may contribute to the development of Peyronie's disease.

Peyronie's disease was first described in 1743 as a form of impotence. Impotence is recognized as one factor associated with the Peyronie's disease, but is not always present. Men most likely to suffer Peyronie's disease often have high blood pressure and high blood cholesterol and uric acid levels, which weaken blood vessel walls.

Men with Peyronie's disease are usually told to live with it unless the erection becomes painful or the bend is so great that the man cannot engage in sexual relations. In general, the goal of treatment is to keep the patient with Peyronie's disease sexually active.

Recent demographic surveys have reported that Peyronie's disease can be found in up to 9% of men between the ages of 40 and 70. The condition is rare in young men but has been reported in men in their 30s. The actual prevalence of Peyronie's disease may be much higher than 9% due to patient embarrassment and limited reporting by physicians.