We carried out postmortem and immunohistological studies of 3 cases of colon cancer in a 14-year-old (case 1) and an 8-year-old girl (case 2), and Turcot's syndrome in a 14-year-old girl (case 3). Tumors were located in the proximal portions of the colon and they were of rare histological types. The expression of proteins--the products of MLH 1, MHS2, and MHS6 genes responsible for DNA reparation was estimated. There was no expression of MLH1 and MHS6 in cases 2 and 3, respectively. The findings enabled the authors to assign these cases to hereditary polyposis-unassociated colonic cancer that is also a variety of Turcot's syndrome.