Burkitt's lymphoma is a childhood disease that characteristically produces large, bulky abdominal tumors. Although these are potentially curable, chemotherapy can produce rapid tumor lysis, with subsequent life-threatening metabolic abnormalities, especially in those patients with large tumors or those who have compromised renal function. Twenty-two patients with proven Burkitt's lymphoma were evaluated by ultrasound. Thirteen patients had abdominal masses. These masses tended to be large, solitary, and acoustically homogeneous. Although most of these tumors were found in the pelvis, upper abdominal and retroperitoneal tumors were also encountered. None of the patients had the typical paravertebral mantle of enlarged nodes seen in other types of lymphoma. In 11 patients with abnormal intravenous pyelograms, ultrasound successfully distinguished between renal lymphoma, hydronephrosis, and, by exclusion, metabolic renal disease. The absence of lymph node disease and the presence of bulky homogeneous extranodal tumor are characteristic ultrasound findings in Burkitt's lymphoma. By locating and quantifying tumor mass and distinguishing between renal lymphoma and hydronephrosis, ultrasound proved to be clinically useful in the management of this disease.