In this article, the Karolinska experience of transrectal fine-needle aspiration biopsy of prostatic carcinoma, which now extends over more than twenty years, is evaluated. The cytologic criteria for diagnosing prostatic carcinoma in aspirates are well defined. While accuracy for cytodiagnosis is similar to that of histopathologic diagnosis, fine-needle aspiration is a less traumatic, cheaper procedure compared with histologic biopsy methods. Accuracy depends very much upon the skill of the examiner taking the cell samples and on the alertness of the cytopathologist for possible diagnostic pitfalls. Cytologic grading of prostatic carcinoma into well, moderately, and poorly differentiated types has been shown to be correlated significantly not only to histopathologic grading, but also to clinical stage, response to hormonal therapy and survival. The degree of tumor differentiation is well reproduced by independent observers. Cytochemical parameters, such as DNA measurement, constitute a potential refinement of cytologic grading, especially in moderately differentiated carcinomas. In medical centers with long experience of fine-needle aspiration biopsy, the method has a central role in diagnosis and management of prostatic carcinoma, including posttherapy follow-up.