The study comprised 1324 carriers (737 females) of MMR gene mutations (500 in MLH1, 648 in MSH2, 117 in MSH6 and 59 in PMS2) from 498 families contributing a total of 58 868 person-years, of which 659 (50%) were diagnosed with CRC, and 1219 non-carriers (712 females) from 287 families contributing 63 436 person-years, of which 36 (3%) were diagnosed with CRC. The gene discussed is PMS2; the disease is colorectal carcinoma.