Concomitant hypo-hyperdontia (CHH) is a rare numeric dental anomaly characterized by congenital missing teeth and supernumerary teeth occurring in the same individual. Due to its rarity and sporadicity, the causes of CHH have been completely unknown. Detailed characterization and presentation of more CHH cases not only strengthen clinical diagnosis and treatment for the patients but facilitate the search for etiological factors of the disorder.From a pedodontic patient population, 21 CHH subjects, with a mean age of 6 years 10 months, were identified and characterized. Dental records and radiographs were scrutinized and analyzed for the distribution and frequencies of involved teeth and concurrent dental anomalies. Through further literature review, 59 CHH cases with supernumeraries in the premaxillary region were retrieved for comparative analyses.The boys were affected twice as often as the girls. While most cases were unrelated and sporadic, two sisters and a pair of identical twins from two unrelated families were presented. Of all cases, only one was of syndromic CHH carrying Duchenne muscular dystrophy. Bimaxillay CHH, with anomalies involving two jaws, occurred more than 4 times as often as maxillary CHH. While all supernumeraries were found in premaxillary region, hypodontia frequently involved lateral incisors and premolars of both jaws.As genetic contribution to CHH is strongly suggested by its familial occurrence and syndromic cases, environmental factors seem to play certain roles in modifying disease phenotypes. Judicious use of radiographs during early mixed dentition stage enhances clinical diagnosis and treatment of CHH.