Mucinous adenocarcinoma of the prostate is one of the least common variants of prostate cancer. The prognosis of this variant of prostate cancer remains controversial. We present 47 cases (1991 to 2006) of mucinous carcinomas treated by radical prostatectomy. Mean patient age at diagnosis was 56 years (range: 44 to 69 y). The mean preoperative prostate-specific antigen (PSA) level was 9.0 ng/mL (range: 1.9 to 34.3 ng/mL). Clinical stages were T1c (34 cases), T2a (7 cases), and T2b (6 cases). The mean percentage of tumor composed of the mucinous component was 52% (range: 25% to 90%). The mean Gleason score was 7 with scores of 6 in 6 cases (12.8%), 7 in 37 cases (78.7%), and 8 in 4 cases (8.5%). Margins were positive in 4 cases of mucinous adenocarcinoma of the prostate. Only 2 cases had isolated margin positivity in the nonmucinous acinar component of cancer. In 12 cases (25.5%), mucinous adenocarcinoma had established extraprostatic extension (EEPE). Eight cases (17.0%) had isolated EEPE of nonmucinous cancer. The 1 lymph node metastasis contained nonmucinous cancer. All together, taking into account both the mucinous and nonmucinous tumor, 20/47 cases (42.5%) had EEPE and 6/47 (12.7%) had positive margins. The 1 lymph node metastasis contained nonmucinous cancer. The mean follow-up for those without progression was 5.6 years (median 6 y, range: 1 to 15 y). One patient (2.1%) progressed 3 years after his radical prostatectomy (5 y actuarial progression-free risk 97.2%). Using the Kattan nomogram, the predicted mean 5-year PSA progression-free risk for nonmucinous prostate cancer with the same PSA and postoperative findings as in the current study was 85.4%. This study confirms that mucinous adenocarcinoma of the prostate treated by radical prostatectomy is not more aggressive, and possibly even less aggressive than nonmucinous prostatic adenocarcinoma.