No established criteria exist for predicting lymphoma grade or transformation in cytologic material. We counted transformed lymphocytes in fine-needle aspiration (FNA) biopsy specimens to determine whether the percentage of these cells in the smear could predict the histologic grade, the biologic behavior, or both.The percentage of transformed lymphocytes out of total lymphoid cells was determined on Papanicolaou-stained smears. Afterward, a cytodiagnosis was based on clinical information available at the time of the FNA, cytomorphologic data, and flow cytometry data. Results were correlated with results of examination of the surgical biopsy specimen, clinical behavior of the lymphoma, or both.The application of fine-needle aspiration (FNA) cytology in the diagnosis and management of malignant lymphoma is still controversial.1-4 Major limitations of this technique include overlap of cytologic patterns between some benign and malignant processes and the inability to determine architectural patterns. 5,6The revised European-American classification system of lymphoid neoplasms (REAL) places a greater emphasis on cytomorphologic examination in combination with immunophenotyping and molecular studies rather than on architectural pattern.7 This new classification system may expand the role of cytology in lymphoma diagnosis, particularly for This research was supported in part by a grant from BristolMyers Squibb, Oncology, Princeton, NJ, and was presented at the 44th Annual Scientific Meeting of the American Society of Cytopathology, November 6-7,1996.Manuscript received December 4, 1996; revision accepted January 23,1997.Address reprint requests to Dr Young: Fox Chase Cancer Center, 7701 Burholme Ave, Philadelphia, PA 19111.The percentage of transformed lymphocytes was 10% or less in all low-grade or indolent lymphomas. Aspirates with transformed lymphocyte counts of 20% or greater were aggressive lymphomas. We also report our experience in the diagnosis of non-Hodgkin's lymphoma by FNA using cytomorphologic examination and immunophenotyping by flow cytometry at a cancer referral hospital. This is a preliminary study, and larger series may help establish the ranges of transformed lymphocyte counts that correlate with the lymphoma subtype.