Thirteen cases of sebaceous gland carcinoma and 10 cases of sweat gland carcinoma were studied using immunohistochemical staining for proliferating cell nuclear antigen (PCNA), c-erbB-2, and p53 to examine correlations among them, and to determine the best predictor of patient prognosis. Many sebaceous gland carcinomas and sweat gland carcinomas showed nuclear accumulation of p53, and patients with tumors showing a PCNA index (percentage of nuclei stained for PCNA) higher than 20%, and a p53 index (percentage of nuclei stained for p53) higher than 10% had short survival. Sebaceous gland carcinomas and sweat gland carcinomas showing c-erbB-2 expression had high PCNA (> 20%) and p53 (> 10%) indices, and were associated with poor prognosis. Histologically, sebaceous gland carcinomas showing a high degree of differentiation and severe nucleolar atypia had high PCNA and p53 indices. A growth pattern of small solid nests and strands, a low degree of differentiation, and the presence of lymphatic permeation in sweat gland carcinoma were often associated with high PCNA and p53 indices. These results suggest that nuclear accumulation of p53 plays an important role in the development of sebaceous gland carcinoma and sweat gland carcinoma. Assessment of PCNA and p53 indices together was very useful for prognostication of patient outcome, using cut-off values of 20% and 10%, respectively, to separate good prognosis from poor. Differentiation of sebaceous gland carcinoma, and c-erbB-2 expression by sweat gland carcinoma were significant independent prognostic indicators.