Familial adenomatous polyposis (FAP) is associated with a number of extraintestinal manifestations, which include osteomas, epidermoid cysts, and desmoid tumors, often referred to as "Gardner syndrome." Recent studies have suggested that some of the phenotypic features of FAP are dependent on the position of the mutation within the APC gene. In particular, the correlation between congenital hypertrophy of the retinal pigment epithelium (CHRPE) and APC genotype indicates that affected families may be divided into distinct groups. We have investigated the association between the dentoosseous features of GS on dental panoramic radiographs (DPRs) and APC genotype in a regional cohort of FAP families. DPRs were performed on 84 affected individuals from 36 families, and the dento-osseous features of FAP were quantified by a weighted scoring system. Significant DPR abnormalities were present in 69% of affected individuals. The APC gene mutation was identified in 27 of these families, and for statistical analysis these were subdivided into three groups. Group 1 comprised 18 affected individuals from seven families with mutations 5' of exon 9; these families (except one) did not express CHRPE. Groups 2 comprised 38 individuals from 16 families with mutations between exon 9 and codon 1444, all of whom expressed CHRPE. Group 3 comprised 11 individuals from four families with mutations 3' of codon 1444, none of whom expressed CHRPE. Families with mutations 3' of codon 1444 had significantly more lesions on DPRs (P < .001) and appeared to have a higher incidence of desmoid tumors. These results suggest that the severity of some of the features of Gardner syndrome may correlate with genotype in FAP.