We identified 58 LS probands; 35 (60.3%) with hMSH2 defects, 20 (34.5%) with hMLH1 defects, and 3 (5.2%) with hMSH6 defects, plus 145 first degree relatives (35 in families with hMLH1, 98 in families with hMSH2, and 12 in families with hMSH6 defects) with a personal history of cancer. The gene discussed is MLH1; the disease is cancer.