We have seen in consultation a variant of atrophy, which is frequently confused with well-differentiated adenocarcinoma of the prostate. We have designated this entity as partial atrophy to distinguish it from its more common counterpart of fully developed atrophy. Partial atrophy is defined as benign prostate glands with relatively scant cytoplasm, yet the glands are not fully atrophic in that they do not appear basophilic at low magnification. Fifty-one cases of partial atrophy were identified (4 from Johns Hopkins Hospital, 47 from consultation). Within the partial atrophy focus, irregular (crinkled) nuclei were frequent in 23.5% and occasionally present in 33.3% of cases. Visible nucleoli were frequent in 25.4% of cases. Basal cells were not identifiable in 27.4% of cases or were hard to identify in 35.3% of cases. No intraluminal crystalloids or blue-tinged mucinous secretion was identified in partial atrophy. Adenocarcinoma or glands suspicious for cancer were present in other cores in 15.6% of cases. More fully developed atrophy was present in simultaneously obtained needle cores in 35.3% of cases. In the cases in which regular atrophy was the only coexisting condition, it was present within one 10x field from the partial atrophy in 22.2%, farther than one 10x field from the partial atrophy in 11.1%, and present in the same gland as the partial atrophy in 66.7%. Partial atrophy may be confused with low-grade adenocarcinoma because of the focus of crowded glands, irregular nuclei, and visible nucleoli. Clues for recognizing partial atrophy include relatively scant cytoplasm, distinct crinkled nuclei, pale cytoplasm similar to adjacent, more recognizably benign glands, and association with more fully developed benign atrophy.