It is occasionally difficult to differentiate between multiple primary and metastatic tumors in case of multiple carcinomas. p53 gene mutation pattern by PCR-SSCP and a clonality analysis on the human androgen receptor gene (HUMARA) in multiple tumors were used to distinguish whether carcinomas were multiple primary tumors or a metastasis. Three female patients with multiple carcinomas, who had undergone surgical resection, were selected for these analyses as typical candidates from 11 cases tested. In the first case with bilateral breast cancer the combined analyses were performed on DNA extracted from tumor portions in paraffin sections of each tumor sample and the results indicated that the carcinomas consisted of a primary carcinoma and metastatic tumors. The carcinomas in the second patient consisted of multiple primary carcinomas and the tumors in the third patient consisted of two independent primary carcinomas with different clonal origins. Thus a combination of p53 gene mutation analysis and clonality analysis on HUMARA provided useful, reliable evidence which can help in discriminating multiple primary tumors from metastatic tumors.