The present study was undertaken to review the pathology of florid papillomatosis (FP) of the nipple and to examine the relationship of FP to breast carcinoma. Clinical features of 49 women studied did not differ appreciably from those noted on prior reports, except that in one instance the lesion was probably congenital. Histologically, three distinct growth patterns were found: sclerosing papillomatosis (17 cases), papillomatosis (12 cases), and adenosis (3 cases). In 17 other cases, mixtures of these proliferative patterns were seen. FP with the sclerosing papillomatosis pattern more frequently had areas of focal necrosis in hyperplastic ducts and scattered mitoses, features that might be interpreted as evidence of carcinoma. No prognostic significance can be attributed to these patterns, since all types were cured by excision with follow-up that averaged 8.3 years. Seven of the 49 women had carcinoma in the same breast as FP: Two women had invasive carcinoma that appeared to arise from FP, and four women had concurrent invasive carcinomas that were separate from the FP; the seventh woman developed diffuse intraductal carcinoma 10 years after FP was excised from the same breast. Three of the seven women were also treated for contralateral breast carcinoma. Also reviewed were lesions from two men who had carcinoma arising in FP. One had intraductal carcinoma with Paget's disease and the other had invasive carcinoma. Appreciation of the diverse histological patterns of FP may be helpful in avoiding an erroneous diagnosis of carcinoma. Features indicative of carcinoma arising in FP are Paget's disease and areas of invasion. FP of the nipple is rarely the substrate for mammary carcinoma and is adequately treated by local excision. Coexistence with carcinoma elsewhere in the same or opposite breast occurs often enough to warrant thorough examination of the breasts when FP of the nipple is diagnosed. The risk of subsequent carcinoma following excision of FP appears to be low, but clinical follow-up is prudent.