IN February, 1936, two sisters, one 3 and one 11 years of age, were referred to the Department of Radiology with the diagnosis of osteogenic sarcoma for roentgen deep therapy following operation. A review of the literature revealed that, last year, Roberts and Roberts (2) were perhaps the first to report the occurrence of osteogenic sarcoma in three members (one brother and two sisters) of the same family. As these authors state, the development of sarcoma in successive generations (3) and in unioval twins has been described (1). Consequently, we thought that it would be of interest to record our observation in the literature. Case 1. Be. R., X-ray No. 5,346, a 3-year-old white girl, was admitted to the orthopedic service (State of Wisconsin General Hospital) on Jan. 17, 1936, with a painful swelling just above the right knee. Three weeks before admission the child had fallen on the right knee and a week later became lame. Roentgenograms taken by the attending physician at home (Fig. 1) were interpreted then as osteomyelitis. This film, as well as another (Fig. 2), taken on Jan. 16, 1936, one day previous to admission to the hospital, shows mottling of the lower end of the femur with definite bone destruction, and an irregular laying down of new bone in the soft tissue. During the next two weeks the pain and swelling increased gradually. Physical examination was negative except for the right leg; there was a hard, fusiform tumor mass at the lower end of the femur. The child had a flexion deformity of 20° at the knee, with a further range of 30°, which was painless. Roentgenograms of the knee showed both a destructive and a productive bone lesion in the lower end of the femur (Fig. 3). The tumor had invaded the soft tissue and there were areas of calcification in the invaded region. Roentgenograms of the chest, skull, and long bones did not reveal any pathologic changes; laboratory findings were not significant. Biopsy was done on Jan. 24, 1936; frozen sections showed an osteogenic sarcoma (Fig. 4). Amputation just below the hip was performed immediately; this was followed by a series of x-ray deep therapy treatments over the stump and right inguinal region from Feb. 12 to 21, 1936. Case 2. Bl. R., X-ray No. 5,337, an 11-year-old white girl, the sister of Case 1, was admitted to the orthopedic service of the State of Wisconsin General Hospital on Jan. 11, 1936, with a history of a small swelling of one month's duration on the ulnar side of the right wrist. It was painful only when bumped or touched firmly. The family physician had been consulted two weeks after the onset. A roentgenogram was taken on Dec. 30, 1935, and a biopsy done on Jan. 12, 1936. The roentgenogram (Fig. 5) showed a destructive bone lesion of the lower 2 inches of the ulna, involving not only the lower shaft, but also the epiphyseal cartilage.