Renal-coloboma syndrome is principally characterized by ocular and renal abnormalities. The PAX2 gene encodes a transcription factor that is expressed in the developing eye, kidney, ear, ureteric bud, and midbrain/hindbrain. Individuals diagnosed with renal-coloboma syndrome present with highly variable clinical manifestations. The most common abnormalities in patients with renal-coloboma syndrome are bilateral optic nerve colobomas and renal hypoplasia with or without renal failure. Patients may also present with auditory abnormalities, urogenital defects causing vesico-ureteral reflux, and central nervous system malformations. The phenotypes among patients can vary both within and between families, and definitive genotype-phenotype correlations have largely been elusive.