Hereditary nonpolyposis colorectal cancer (HNPCC) (MIM #114500), also called Lynch syndrome, is an autosomal dominantly inherited cancer syndrome accounting for 1-5% of all colorectal cancer cases. In a study of three Korean families with HNPCC consistent with the revised Bethesda criteria, DNA testing revealed three novel HNPCC germline mutations in two genes: namely, MLH1, with an insertion resulting in a frameshift and a premature stop codon; MSH2, with a deletion at nucleotide 633, exon 3, which results in stop of translation at codon 213; and MSH2, with a deletion at nucleotide 1413, exon 9, resulting in a frameshift and a premature stop codon. In the first two families, there were splice mutations at c.2006-6 thymine to cytosine. The clinical implications of a frameshift mutation are discussed, along with the significance of common underlying splice mutations existing within families with HNPCC.