We investigated the incidence of granuloma and its related factors in 180 patients with prostate cancer who showed subcutaneous granuloma formation during androgen deprivation therapy with subcutaneously administered leuprorelin acetate. A granuloma was defined as a persistent induration over 30 mm in diameter in the injected portion. Small indurations which often developed and disappeared after every injection were excluded. The survey was performed using a questionnaire after receiving written informed consent. Among the 180 patients with prostate cancer, 21 (11.7%) developed a granuloma at the injection portion, and subsequently the injection of leuprorelin acetate had to be discontinued. Eighteen of the 21 patients alternatively received goserelin acetate. Three patients had high-grade granulomas with ulcer and abscess formation, and were successfully treated with oral antibiotics. The average duration between the first injection of leuprorelin acetate and granuloma formation was 20.2 months (range : 4 to 62 months). There was no association between granuloma formation and patient backgrounds, such as allergic predisposition and past history. Twenty-one of the 180 prostatic cancer patients developed subcutaneous granuloma induced by the injection of leuprorelin acetate. The investigation showed an unexpectedly high incidence of granuloma formation. We must explain the risk of developing subcutaneous granuloma to the patients before introducing leuprorelin acetate.