Neoplasms were found in 19 of 170 cottontail rabbits (Sylvilagus floridanus mearnsii) necropsied at the Wildlife Pathology Laboratory, Michigan Department of Conservation, 1950–1966. Nine tumors were benign; eight fibromas and one lipoma. Six malignant lymphomas, one nephroblastoma and three undiagnosed but apparently malignant tumors, also were found. Of particular interest is the high ratio of malignant to benign neoplasms. Gross and microscopic characteristics for the neoplasms are described and a case history involving a malignant lymphoma is discussed.