Hereditary Amelogenesis Imperfecta (HAI) is a hereditary dental enamel disorder showing a varying clinical picture. Reviewing the literature, there seems to be a need for a better knowledge in many aspects concerning this disorder, not least to enhance the therapeutical approach for individuals suffering from HAI. The aims of this thesis, were to identify and to classify hereditary enamel defects and to estimate their prevalence in a Swedish child population. The oral health of individuals diagnosed as having HAI was also analysed and evaluated. 425 000 children, from the western part of Sweden, aged 3-19 years, were screened in order to identify individuals showing enamel defects of hereditary linkage. In this way, 105 children were identified. They were clinically classified into 12 different subgroups. Genetic analyses were also made. In 99 children, the oral health status was analysed and evaluated. In another patient material, 26 individuals aged 8-20 years and with HAI, the anterior open bite malocclusion was studied. The prevalence of HAI was estimated to be 1 case in 4000. In analyses of genetic data, eight different subgroups of HAI were identified based on the two major types, the hypoplastic and the hypomineralized. The hypoplastic, rough-pitted type with autosomal dominance, represented the most common HAI disorder. A low caries susceptibility was found in children with severely hypoplastic and hypomineralized enamel. Bacteriological and salivary data in the children could not fully support the findings regarding the low caries susceptibility. A high number of restorations were recorded predominantly in severe cases of the hypomineralized type, in which group gingival inflammation, plaque and dental calculus also were frequently found. The open bite occlusion could be associated both with the hypoplastic and the hypomineralized types of HAI. This malocclusion was considered to be of skeletal origin. The prevalence found shows that HAI is a fairly common enamel disorder with a varying clinical expressivity. The oral health findings in individuals suffering from the disorder indicate a need for early treatment planning.