An 8-year old boy was referred to the orthodontic department because of a fused tooth. The clinical and radiological examination showed that - besides the double tooth at the region of the 21 - there was a normal tooth 22 in eruption as well. Moreover a still impacted supernumerary tooth was present in the right upper front region. The treatment included the extraction of the fused tooth and an autotransplantation of the supernumerary tooth to the extraction site of the fused tooth. During the follow-up period the pulp showed a progressive obliteration starting at the crown level with a conservation of the vitality. Apexification of the root of the transplanted tooth proceeded successfully. Furthermore a review of the literature is given in this article on the aetiology and treatment of fused teeth and on the application of autotransplantation.