The clinical and laboratory findings in 106 patients with Peyronie's disease as well as histopathological examinations of biopsies from the plaques were studied. The clinical symptoms and signs were in general similar to those found in previous studies, but bone marrow smears showed an increased number of plasma cells and lymphocytes in 18 of 24 examined. Biopsy of the plaque in cases of long-term symptomatology disclosed a fibrosis poor in cellular components. In patients with a short history of the disease and a tender induration, an inflammatory component of the specimens with perivascular accumulation of lymphocytes and balooning of endothelial cells in the small vessels was seen. Characteristic cells with "cross-banded" nuclei, described earlier only in Dupuytren's contracture and experimental fibrosis, was observed for the first time in Peyronie's disease. Based on these findings a combined traumatic-immunological etiology is suggested.