Objectives. To report on a case of mucinous carcinoma of the prostate and discuss the clinical and histopathologic features of the mucin-producing carcinoma of the prostate from a review of published reports. Methods. Our case and 87 other previously reported cases were evaluated clinically and histologically. Results. We encountered a case of mucinous carcinoma of the prostate, Stage C, which was treated by radical prostatectomy. After reviewing it and the 87 other cases, we believe that these cases of mucin-producing carcinomas can be divided into three groups: 60 cases of mucinous carcinoma, 17 cases of primary signet-ring cell carcinoma, and II cases of mucinous carcinoma with signet-ring cells. Mucinous carcinoma is a variant of high-grade adenocarcinoma of the prostate, wherein there is a 77.8% rate of prostate-specific antigen elevation and a similar rate (77.8%) of response to endocrine therapy. Fifty percent of patients survived 3 years and 25%, 5 years. In contrast, primary signet-ring cell carcinoma conveys one of the worst prognoses among patients with prostate cancer. There are no reliable tumor markers, and there was no response to endocrine therapy. Patients with primary signet-ring cell carcinoma had a 27.3% 3-year survival rate; none survived to 5 years. The clinical features of mucinous carcinoma with signet-ring cells are very similar to primary signet-ring cell carcinoma; again, there was no response to endocrine therapy and the 3-year survival rate was 16.7%. Conclusions. Although it has been suggested that mucinous carcinoma is a variant of high-grade adenocarcinoma of the prostate, signet-ring cell carcinoma and mucinous carcinoma with signet-ring cells are other variants of carcinoma that develop in the prostate, and their prognoses are very poor. UROLOGY 54: 141-144, 1999. (C) 1999, Elsevier Science Inc.