We present a 53-year-old man with a multilocular solid and cystic mass measuring 19 cm on cross-sectional imaging. After undergoing pelvic mass excision, final histopathology confirmed the diagnosis of primary prostatic stromal tumor of uncertain malignant potential (STUMP). Prostatic STUMPs are rare mesenchymal tumors with diverse histologic patterns. They are distinct from prostatic stromal sarcomas as they do not behave aggressively, although some may occasionally demonstrate local recurrence after resection. Due to their unpredictable malignant potential, lack of correlation between histologic patterns, and sarcomatous differentiation, these patients warrant surgical excision and close follow-up.