An intensive study of the family history of cancer in 4,515 patients screened consecutively by a multiphasic mobile cancer detection unit showed, after age correction, that cancer had developed in 8.9% of the probands when there was one cancer in a single first-degree relative, 16.2% had cancer with two family members affected, and 27.4% had cancer when three or more family members had been affected. This constituted a significant correlation between family and personal histories of cancer in these patients. Extrapolation to the United States population with cancer-control implications are given.