The aspiration biopsy cytology of 11 prostates obtained at autopsy from men younger than 40 yr old were studied to define the cytologic criteria of benign changes in this age group. Cytologic features that differ from those of older men with benign prostatic enlargement include abundant cellularity, the presence of large and small cell groups (which would otherwise suggest dyshesion), and a predominantly columnar cell shape. These differences can be attributed to age-related changes in the prostate. A case of a prostatic nodule in a 22-yr-old that was evaluated by fine-needle aspiration biopsy is presented to illustrate the diagnostic difficulties that can arise when the interpreter is unaware of differences in cytologic patterns due to age.