Proliferative breast disease (PBD) is a well-recognized histologic entity that has received increasing attention in the cytologic literature. We have attempted to prospectively identify and subclassify PBD by fine needle aspiration biopsy since 1987 using criteria we developed through our experience. Over 2800 breast FNABs were performed on breast lesions from 1987 to mid-1992; 257 were cytologically diagnosed as PBD with or without atypia. Eighty-four were significantly worrisome clinically to warrant surgical excision. Forty of these were designated PBD without atypia by cytology; 23 (58%) were in agreement with histology; three (8%) were PBD with atypia by histology; five (13%) were cancers; and nine (22%) were nonproliferative. Forty-four cases were designated PBD with atypia; 24 (55%) were in agreement with the histologic diagnosis; 12 (27%) proved to be PBD without atypia; six (13%) were carcinoma; and two (5%) were nonproliferative. After 1991 we employed stricter criteria for PBD, improving on the results from 1991-1992. During this period, there were 53 diagnoses of PBD with or without atypia and 34 were excised. Nine of the 10 (90%) aspirates designated as PBD without atypia were in agreement with histologic findings. The other case was nonproliferative. Fifteen of the 24 cases diagnosed as PBD with atypia were in concordance with histologic findings (63%), one was nonproliferative, seven were PBD without atypia (29%), and one (4%) proved to be carcinoma.(ABSTRACT TRUNCATED AT 250 WORDS)