The value of fine-needle aspiration biopsy of carcinoma of the prostate and its cytological grading is demonstrated. The grade of morphological differentiation in cytological smears has proved to be a reliable criterion for the prognosis in 496 estrogen-treated prostatic carcinoma patients. The life expectancy of low-differentiated and anaplastic cancer patients undergoing treatment is so poor that the justification for antiandrogen treatment in this group of carcinomas appears extremely doubtful. For this reason, the degree of differentiation of the tumor should be considered when undertaking therapeutic measures in view of its relevance for the prognosis.