Subject of our research were etiology and frequency of hypodontia and the possible effects of hypodontia on correct formation of dental arches in the course of dentition development. Methodologically the diagnostic records of 3238 patients of an orthodontic practice in Magdeburg, Germany, were evaluated. In addition to determining the frequency of hypodontia (8.1%), special attention was paid to accompanying micro-symptoms. 169 family members of 35 patients with teeth aplasia were questioned and examined and then extended family tables were drawn up. In addition, 105 dental casts from both patients with aplasia and patients with full dentition were measured. The results thus obtained made possible a comparison of the teeth and jaw size of the group with hypodontia with the group without hypodontia.