We report three cases of endometrioid adenocarcinoma of the prostate. Case 1: A 71-year-old male was admitted with a complaint of micturition pain. Serum prostatic specific antigen (PSA) was 12 ng/ml. Radical prostatectomy following needle biopsy was performed in May 1998. Histopathological diagnosis was prostatic endometrioid adenocarcinoma (pT2bpN0M0). Case 2: A 71-year-old male was admitted with a complaint of macrohematuria. PSA was 18 ng/ml. Cystoprostatectomy and ileal conduit construction following needle biopsy were performed in July 2002. The tumor that was diagnosed as endometrioid adenocarcinoma, invaded the bladder neck (pT4pN0M0). Case 3: An 86-year-old male was referred to our department for elevated PSA (16.8 ng/ml). Prostatic needle biopsy was performed and histopathological diagnosis was endometrioid adenocarcinoma with a part of well differentiated adenocarcinoma (T2bN0M0). PSA dropped to an undetectable range after total androgen blockade therapy.