METHODS.Fifty-one air-dried, Diff-Quik-stained fine-needle aspirates (FNA) of palpable breast lesions with biopsy-proven diagnoses of NPBD (34 cases) or PBD 1 Department of Pathology, The George Wash-(17 cases) were reviewed. The smears were evaluated for the cellularity, size, and ington University Medical Center, Washington, architectural arrangement of the epithelial groups; the presence of single epithelial DC.cells and myoepithelial cells; and nuclear characteristics. 2 Department of Surgery, The George Washing- RESULTS.The only cytologic feature found to be significantly different between ton University Medical Center, Washington, DC.PBD and NPBD was a swirling pattern of epithelial cells. A swirling pattern was noted in 13 of 17 PBD cases (76%) and 12 of 34 NPBD cases (35%) (P Å 0.008). CONCLUSIONS. Because there is significant overlap in cytologic features between NPBDand PBD, the distinction between the two entities is difficult in cytologic sampling.