We present the case of a 20-year-old male with a clinicalpresentation of both glioblastoma multiforme and multiple adenomatous colonic polyps.The molecular genetics study revealed a mutation in KrasAsp12 gene and altered expression of HMSH2 and HMSH6 proteins encoded by the DNA mismatch repair genes in two of the colonic polyps. This evidence concerns the gene MSH2 and glioblastoma.