A retrospective literature review was carried out to determine the prevalence of hypodontia and current knowledge of associated etiological factors. Reported studies vary widely in their reports of prevalence. The majority are retrospective radiographic studies, and reported rates vary from 2.6% to 11.3%. Racial differences have been determined: in Caucasian studies the mandibular second premolars and maxillary lateral incisors were the most frequently recorded absent and in Asian studies, the mandibular incisor was the most frequently recorded absent. Prevalence rates are higher in females compared to males (3:2, respectively). The association of hypodontia with other systemic conditions and dental anomalies is widely reported. Hypodontia can be regarded as a multifactorial condition. Recent developments in molecular genetics have established the importance of the muscle specific homeobox genes (Msx1 and Msx2) in dental development. Specific genes that are responsible for the more severe types of hypodontia, including ectodermal dysplasia, have been identified by linkage analysis. However, variable expression of the trait suggests a polygenic mode of inheritence with epistatic genes and environmental factors interacting.