PURPOSE: To report a novel sporadic PAX2 gene mutation in a child with atypical bilateral optic nerve coloboma and congenital renal hypoplasia. DESIGN: Observational case report and experimental study. METHODS: Mutational analysis of the PAX2 gene in a family. RESULTS: A 9-year-old patient with a history of renal transplantation for congenital renal hypoplasia was found to have bilateral optic nerve coloboma during ophthalmic examination for cytomegalovirus retinitis. A previously unreported mutation in exon 2, delT 602 leading to a prematurely truncated protein was identified in the child but in neither of her parents, demonstrating a de novo mutation or germline mosaicism. CONCLUSIONS: The causal relationship between PAX2 gene mutations and renal-coloboma syndrome is further supported by this novel mutation. Awareness of the systemic associations with optic nerve abnormalities and the ocular findings in syndromic renal diseases will facilitate the management of these highly variable disorders.