Adenocarcinoma of the prostate in a 41-year-old man with XXY karyotype and chronic lymphocytic leukemia: report of a case. We report a case of adenocarcinoma of the prostate in a 41-year-old man with 47XXY karyotype (Klinefelter's syndrome) and chronic lymphocytic leukemia. The increased incidence of malignancy in individuals with Klinefelter's syndrome has been well documented for certain neoplasms. Adenocarcinoma of the prostate has not been reported previously in a patient with Klinefelter's syndrome and a 47XXY karyotype. Absence of mosaicism was confirmed by peripheral lymphocyte, skin fibroblast, bone marrow cell and spleen stroma fibroblast cultures. Chronic lymphocyte leukemia, especially the T-cell cytotoxic/suppressive variant, may additionally add to an immunological deficit. Since carcinoma of the prostate, Klinefelter's syndrome and chronic lymphocytic leukemia are common, the lack of a previous report is interesting. Etiological aspects are discussed. 