PURPOSE: This paper describes the screening of eight patients with severe oligodontia for PAX9 and AXIN2 mutations. SUBJECTS AND METHODS: Anamnestic data and a panoramic radiograph were collected to study the phenotype of eight patients with oligodontia and their first-degree relatives. A blood sample was taken for a mutational screening for PAX9 and AXIN2 mutations. RESULTS: No mutations were discovered, but a unique nucleotide change in a conserved 5' flanking region of PAX9 was revealed. Earlier screening of the same patients for MSX1 mutations also had a negative outcome. CONCLUSIONS: Considering the discrepancy between the high incidence rate of agenesis and the relatively small number of reported causative mutations in PAX9, MSX1 and AXIN2 genes, the genetic contribution to oligodontia probably is much more heterogeneous than expected so far. Therefore negative results, like the present exclusion data, should be published more often in order to get a better appreciation of the relative contribution of these specific mutations causing oligodontia. In this context the exact number of tested probands also should be mentioned at all cases. Recent evidence of PAX9-MSX1 protein interactions in odontogenesis as well as other genes and developmental factors should receive more attention.