Tricho-dento-osseous dysplasia is a rare autosomal dominant disorder which involves increased bone density, enamel hypoplasia, enlarged pulp chambers, and molar taurodontism. This study discusses the phenotypic variability of this condition and describes 3 new cases from a large family.Three affected females and 1 unaffected female from the same family were clinically and radiographically evaluated. Mutation analysis was performed in the candidate gene DLX3. Phenotypes of affected individuals from 3 generations were compared to an unaffected control.All affected subjects show increased bone density in long bones and increased thickness and bone density in the skull, especially the skull base. Mandibles are within the upper normal size limits and display increased trabeculation and bone density. No bone loss or regression of the alveolar ridge occurs in older subjects after teeth have been lost.The mutation in DLX3 has positive effects on bone density throughout life. Although the mutation in this family is identical with mutations found in other families it results in clinical and phenotypic variability.