The data of clinical examination, diagnostic models and panoramic x-rays investigation of the 332 patients at the age from 6 to 18 years with adentia were analysed. The congenital absence of more than 6 teeth was defined as oligodontia. The purpose of the study was to evaluate the prevalence of missing teeth patterns and other dental abnormalities such as microdontia, persistent deciduous teeth, ankylosis, taurodontism, impaction and transposition in children and adolescents with isolated and syndromic oligodontia to optimize the diagnostic and orthodontic treatment plan. The total number of 332 patients were devided into three groups: 1-132 patients with hypodontia, 2-119 subjects with isolated oligodontia and 3 - 81 with syndromic oligodontia. The subgroup comprised of 45 children with ectodermal dysplasia (ED) syndromes and oligodontia 1,5-6 years at baseline examination was selected from the patients of group 3. The main type of inheritance was X-linked recessive and the most spread syndrome was hypohidrotic ectodermal dysplasia or Christ-Siemens-Touraine syndrome. The female patients were twice more than males in hypodontia and isolated oligodontia groups, but in group of 3 syndromic patients the rate of males to females was 1,56:1. The most stable to agenesis teeth were the upper central deciduous and permanent incisors. In group 2 the most often absent teeth were upper second premolars and in group 3-the upper lateral incisors. In syndromic patients with temporary dentition the upper lateral incisors and all lower incisors were always absent. It was concluded that the absence of teeth at the age of 1,5 years, male gender and absense of more than 14 teeth in the temporary dentition and 20 teeth in the permanent dentition were the signs of syndromic oligidontia. It is necessary for such patients to be examined besides dentists and pediatrician by other medical specialist such as dermatologist and geneticist.