The majority of patients with incontinentia pigmenti (IP) have a mutation in the nuclear factor-kappa-beta essential modulator (NEMO) gene, and mice with a targeted deletion of NEMO exhibit skin pathology remarkably similar to the human disease. This study characterizes the retinal vascular abnormalities of NEMO-deficient mice, and compares this phenotype to known features of human IP. Nineteen heterozygous NEMO-deficient female mice, ages ranging from post-natal day 8 (P-8) through 6.5 months of life, were studied. Eyes were sectioned and stained either whole or as retinal flat mounts after incubation for enzyme histochemical demonstration of ADPase, which labels the vasculature. With maturation, retinal arteriolar abnormalities became evident at 3 months of age. Global assessment of the retinal vasculature with ADPase staining showed increased vascular tortuosity. Microscopic examination of sections of ADPase-incubated retinas revealed arteriolar luminal narrowing due to endothelial cell hypertrophy and increased basement membrane deposition. Venous morphology was normal. This study characterized the histological retinal phenotype of heterozygous NEMO-deficient female mice. Most striking were retinal arteriolar abnormalities, including luminal narrowing, endothelial cell hypertrophy, and basement membrane thickening. Retinal flat mounts revealed arteriolar tortuosity without evidence of vaso-occlusion or neo-vascularization.