Gardner's syndrome (GS) is a very rare autosomal dominant multisystem disease. Osteomas, skin and soft tissue tumors are present with gastrointestinal polyposis. The polyps have very high malignancy potentials. If prophylactic resection is not performed, colorectal cancer development is inevitable in all patients with GS. Polyposis is usually asymptomatic. Therefore, careful evaluation of extraintestinal findings of the disease is very important for early diagnosis. In this article, diagnosis and treatment of GS are presented in monozygotic twins, which have not been previously described in the literature. The diagnostic process, which started with dental complaints of one case, was carried out in an effective manner and then, prophylactic surgery was performed in twins. This article aimed to make clinicians and dentists attentive for early diagnosis of disease and to review treatment options.