Sixty-six children (forty-one boys and twenty-five girls) were evaluated for differences in characteristics of premaxillary hyperdontia between the primary and permanent dentitions. The study population had forty-five supernumerary teeth in their primary dentitions and fifty supernumerary teeth in their permanent dentitions. Eighty percent of the primary supernumerary teeth were located in the lateral incisor regions, in proper alignment within the dental arch. Sixty-two percent of the supernumerary teeth in the permanent dentitions were situated in the central incisor regions; 90 percent were outside the dental arch, mostly palatal; and 42 percent were inverted. Seventy-three percent of the supernumerary teeth in the primary dentitions had erupted. Twin tooth formation occurred in twenty-eight patients, the majority in the primary dentition; but in eleven children, both dentitions were involved. Interference with the normal dentition occurred most often in the permanent dentition. Children with primary supernumeraries exhibit a greater chance of hyperdontia in the permanent dentition than do others.