Thirty-seven cases of juvenile papillomatosis of the breast were reviewed. The average age was 19 years (range 10-44 years). On examination the patients usually had a localized, multinodular mass that was interpreted as a fibroadenoma. Microscopically, typical lesions featured papillomatosis, sometimes with severe atypia, cysts with or without apocrine metaplasia, duct stasis, and sclerosing adenosis. In one case the breast with papillomatosis adenosis. In one case the breast with papillomatosis has remained free of carcinoma, but at the time of biopsy the patient had secretory carcinoma of the other breast. Papillomatous changes were not observed in the breast with carcinoma. Another woman had lobular carcinoma in situ coexisting with juvenile papillomatosis. After an average follow-up of 8 years, no subsequent carcinoma has been found. Thus, there appears to be little risk for early onset of carcinoma, but without additional follow-up the long-term assessment of this disorder remains uncertain. We recommend that a patient with juvenile papillomatosis have a thorough clinical examination of the breasts at least once a year.