We report a case of Burkitt's lymphoma, which was suspected to involve both breasts. US showed a replacement of the normal breast tissues by a diffusely mixed or mottled pattern of echo texture, associated by hypoechoic cyst-like masses with slight internal echogenicity. This pattern was indistinguishable from the sonographic changes produced by a mastopathy. These findings disappeared after successful chemotherapy for the Burkitt's lymphoma, suggesting that the ultrasonographic pattern of mastopathy was caused by the infiltration of the breast tissues by the lymphomatous cells.