Gardner's syndrome (familial polyposis coli) is a genetic condition characterised by colonic polyps that carry a 100% risk of malignancy if untreated. Early diagnosis, in which an astute and knowledgeable dentist can play an essential role, is therefore of paramount importance. The presence of multiple unerupted teeth provides the dentist with a major pointer to the possible presence of this disease, which may be provisionally diagnosed on the detection of two other obvious features, namely osteomas and cutaneous lesions. This fact is clearly illustrated by the accompanying case report. Extracolonic manifestations increase the morbidity and make treatment more difficult. The presence of large desmoid tumours may be a serious complicating factor. Gardner's syndrome may be accompanied by adenomas of the stomach and duodenum and very rarely by malignant tumours of the central nervous system. Regular surveillance by means of colonoscopies must be carried out on all individuals suspected of having the disease in order to implement timeous life-saving prophylaxis.