Peyronie disease, or (abnormal) curvature of the penis, is the hardening of the dorsum of the penis of unknown cause. Histologic in the early stage, there is perivascular chronic inflammatory infiltrate between the tunica albuginea and the sinusoids of the corpora cavernosa and endothelial cell hyperplasia. Over time, there is proliferation of the fibroconnective tissue and rarely ossification. The tunica albuginea is the membrane that encapsulates the spongy chambers (corpora cavernosa) of the penis. Corpora cavernosa is a mass of erectile tissue with large interspaces capable of being filled with blood. One of the functions of the tunica albuginea is to facilitate the trapping of blood in the corpora cavernosa, thereby maintaining erection of the penis.

The disease is uncommon. It usually affects men between 40 and 60 years of age. Patients who have undergone treatment for prostate cancer (surgery or radiation) are at increased risk, as are those who have had a penis fracture / sexual intercourse injury of the penis. There is some evidence that predisposition to the condition may be inherited. A small portion of patients with Peyronie disease also develop Dupuytren's contracture.