Specialized stromal tumors of the prostate encompass stromal sarcoma and stromal tumors of uncertain malignant potential (STUMP). As a result of their relative rarity and lack of long-term follow-up, the prognosis of STUMP is unclear. We studied 50 cases of STUMP and stromal sarcoma with regard to their clinical presentation and follow-up. Patients ranged in age from 27 to 83 years (mean 58 years). The major presenting signs and symptoms were urinary obstructive symptoms (n=25), abnormal digital rectal exam (n=15), hematuria (n=7), hematospermia (n=1), and rectal dysfunction/fullness (n=3). An elevated prostate-specific antigen was either the sole or a compounding rationale for initial urologic examination and prostate biopsy in a subgroup of patients (n=11). The histology in the 36 cases of STUMP not associated with sarcoma were as follows: 25 composed of stroma with scattered cytologically atypical cells associated with benign glands; 8 resembling glandular-stromal hyperplasia but with hypercellular stroma; 6 with extensive myxoid stroma; and 1 with phyllodes pattern. Four of these cases had mixed patterns. Seven cases of STUMP were associated with sarcoma, either concurrently or subsequently. In another 7 cases, pure sarcomas were encountered: 3 low grade (LG) and 4 high grade (HG). In 19 STUMPs, the location of the lesion was determinable: 10 cases arose in the peripheral zone, 7 cases were located in the transition zone, and 2 cases seemed to involve both zones. In 3 of these cases, tumors were adherent to the rectum at the time of resection. There was no evidence of progression of disease for 14 STUMPs after biopsy, TUR, or enucleation where follow-up ranged from 0.3 to 14 years (mean 4.9 years). Five cases of STUMP showed local tumor growth: 1 case increased in size from 6 to 7.5 cm in 3 years and 4 cases recurred frequently necessitating multiple TURs of the prostate (n=2, n=3, n=3, n=3) over 1.1, 2, 7, and 8 years, respectively. Fourteen patients with STUMP underwent radical prostatectomy (RP) soon after diagnosis; of these, 12 were organ confined where the tumor size ranged from 0.7 to 7.5 cm (mean 2.7 cm); 2 cases with a history of a 28 g TUR and a 275 g enucleation showed no residual tumor in the RP specimen. Three cases were lost to follow-up. The histologic subtypes of STUMP did not correlate with the clinical behavior or likelihood of being associated with sarcoma. Two of the LG sarcomas locally invaded around the seminal vesicle, yet all of the LG sarcomas with follow-up were free of disease at 3, 13, 24, 25, 30, and 36 months. Of the 6 HG sarcomas with follow-up, 3 were free of disease at 3, 17, and 72 months. One man was alive with metastasis to the lung 10 months after RP, 1 man was alive at 280 months with multiple metastases, and another died of disease at 115 months. STUMPs can recur frequently, occur at a young age, often involve the peripheral zone where they can be adherent to the rectum requiring its removal, and can be associated with stromal sarcoma. Although STUMPs can be histologically misdiagnosed as nodular hyperplasia, it is important to recognize that these are neoplasms with unique local morbidity and malignant potential. Whereas LG stromal sarcomas can locally invade, HG sarcomas can metastasize and lead to death.