AbstractFine‐needle aspiration cytolotogy (FNAC) is an acknowledged method for diagnosing prostate cancer. False‐positive results are uncommon, but concerns have been raised that prostatic intraepithelial neoplasia (PIN) could be misinterpreted as carcinoma. Therefore, we attempted to describe cytological features of PIN. Cells were scraped from macroscopically normal areas of 177 radical prostatectomy specimens, smeared and Giemsa‐stained. Histological slides from these areas were reviewed, and 17 samples with high‐grade PIN and with no invasive cancer were selected. Smears from 17 invasive cancers were used for comparison. Cancer showed high cellularity and dissociation, while PIN smears only contained a few clusters of atypical cells. Pronounced nuclear atypia, prominent or multiple nucleoli and mucin were more common in cancer, while cytoplasmic granules, crystalloids and cluster size did not distinguish between PIN and cancer. In conclusion, PIN should not be diagnosed by FNAC alone. However, a highly cellular smear with pronounced atypia seems to preclude PIN. Diagn. Cytopathol. 2006;34:317–322. © 2006 Wiley‐Liss, Inc.