Aim: To determine if the variable expression of tooth agenesis in a family whose members all presented with multiple and variable tooth agenesis is related to a mutation of the PAX9 gene. Methods: The family was examined and its histories recorded. A buccal cheek swab was used to isolate DNA and sequencing of the PAX9 gene was performed. Results: All family members had a homozygous point mutation at the 718 position (G to C) in exon 3 (a nonpaired domain) of PAX9. Conclusion: The variable expression of tooth agenesis in this family suggests that clinicians should carefully examine all members of a family in which tooth agenesis is identified. World J Orthod 2008;9:412.e55–61.