Taurodontism and a reduced tooth length are reported to occur in patients with oligondontia. The aim of this study was to evaluate the occurrence of these factors in Dutch patients with oligodontia. Panoramic radiographs of 117 patients with oligodontia and 91 controls were collected. Taurodontism of the mandibular first molars was recorded and the length of cuspids, bicuspids and first molars of the mandible were measured. In patients with oligodontia 28.9% showed taurodontism of one or two mandibular first molars. The prevalence of taurodontism in normal Dutch subjects was 9.9%. No significant differences were found between the two sexes in both groups. Neither was there a significant difference in the unilateral and bilateral occurrence of taurodontism. The present findings supported the hypothesis that taurodontism may be the result of an ectodermal defect and a manifestation of developmental instability in patients with oligodontia. The length of mandibular cuspids and first molars in females were significantly reduced. In males only the lower right first molar was significantly reduced. The reduced length of the teeth may also be the result of a defect in ectodermal cells. Both taurodontism and a reduced length are of importance considering dental therapy.