The APC gene was investigated in 31 unrelated polyposis coli families by SSCP analysis and the protein truncation test. Twenty-three germline mutations were identified which gave rise to a variety of different phenotypes. Some of these mutations have already been described; however we report six previously unpublished mutations. Typical disease symptoms were observed in families who harboured mutations between exon 4 (codon 169) and codon 1393 of exon 15. Mutations beyond codon 1403 were associated with more varied phenotype with respect to the development of extracolonic symptoms. In this report we provide support for the notion that there appears to be a correlation between the location of an APC mutation (beyond codon 1403) and extracolonic manifestations of familial adenomatous polyposis.