&NA;Orthopantomograms of the mandible were performed on 46 patients with familial polyposis coli having no clinical signs of Gardner's syndrome and on 46 control patients matched according to age and sex. Thirty‐five patients (76.1 per cent) and two (4.3 per cent) controls had osteomas (P<0.0005). It is concluded that orthopantomography of the mandible is a valuable diagnostic supplement to prophylactic proctosigmoidoscopic examination of first‐degree relatives of polyposis patients. Due to the frequent occurrence of mandibular osteomas in polyposis patients without clinically detectable extracolonic manifestations, it is suggested that “Gardner's syndrome” is no longer considered a clinical entity.