The presence of a fifth mandibular incisor, a eumorphic supernumerary tooth, has rarely been described in the literature. Recently we reported on a large Lebanese consanguineous family where 4 individuals displayed 5 mandibular incisors with the same shape and size. This type of familial clustering of the trait has not been previously described. We previously postulated several theories to explain the etiology of this anomaly. The possibility of an autosomal recessive inheritance for this nonsyndromic trait was discussed. We now report the use of homozygosity mapping to identify a homozygous region with different alleles at chromosome 16q12.2, located at the marker D16S415, which likely harbors the gene underlying this anomaly.