Twenty cases of granulomatous prostatitis are presented. They were identified, histologically or cytologically, among 1,316 patients with prostatic pathology at the General Hospital of Asturias during a period of 3 years (Jan. 1984 to Dec. 1986). The etiology, histogenesis, clinical and morphological aspects, treatment and prognosis of the different types of granulomatous prostatitis, according to a classification by the authors, are discussed. The significance of the differentiation of granulomatous prostatitis from carcinoma is discussed. Fine-needle aspiration cytology (Franzen) is recommended as the diagnostic method of choice.