The American form of Burkitt's lymphoma is a high-grade malignancy which usually involves the abdomen in children and young adults. There is only a limited literature which describes the cytologic features of Burkitt 's lymphoma in serous effusions. We present three children with Burkitt's lymphoma initially diagnosed by effusion cytology. The first patient, an 11-yr-old boy, presented with bilateral pleural effusions, ascites, and abdominal masses and had diagnostic pleuralfluid cytology without tissue confirrnation (ultrastructural examination was performed on the effusion specimen). He died 7 months after the initial diagnosis. The second patient, a 9-yr-old boy, presented with ascites and abdominal masses and had diagnostic peritoneal fluid cytology with a subsequent confirmatory chest wall biopsy. The third patient, a 16-yrold girl, presented with a 2-month history of irregular menses, a large pelvic mass, lymphadenopathy, and liver masses. Although an ovarian malignancy was clinically suspected, cytoIogic examination of herperitonealfluid revealed Burkitt's lymphoma. Surgical exploration revealed involvement of her right ovary, cecum, and terminal ileum. The second and third patients are currently alive with no apparent disease following chemotherapy. In all three patients, effusion cytology revealed Burkitt's lymphoma, characterized by a uniform population of noncohesive lymphoid cells with noncleaved nuclei, prominent multiple nucleoli, and scanty-to-moderate basophilic cytoplasm. Cytoplasmic and/or nu- clear vacuoles were also seen, more promineni in Diff-Quiksiained, air-dried smears. These cases demonstrate the importance of recognizing the cytologic features of Burkitt's lymphoma, as serous fluid may be the initial diagnostic specimen. Diagn Cytopathol 1995; 12:3-7.