OBJECTIVE To determine whether contact lens, related corneal pannus regressed when eyes were refitted with rigid gas-permeable contact lenses and to investigate the role of hypoxia as the putative origin of this complication. METHODS Twenty-three eyes of 14 patients with corneal pannus were identified retrospectively from a referral practice population and were separated into two subgroups. One subgroup accepted refitting with rigid gas-permeable contact lenses or discontinued contact lens wear, and the other elected to continue wearing hydrogel or polymethylmethacrylate contact lenses. The response of pannus was observed by slit-lamp biomicroscopy and photographs and was compared between the two subgroups. One eye of each of six patients identified with bilateral corneal pannus secondary to daily wear of hydrogel contact lenses was selected at random. Duplicates of the hydrogel contact lenses worn by these eyes were obtained, and their peripheral oxygen transmissibility (Dk/Lp) values were compared with those of a control group of hydrogel contact lenses identical to those worn by another group of patients, matched by age, gender, and laterality to the study group, but who did not have corneal vascularization. RESULTS Vascularization regressed in 14 eyes of nine patients refitted with rigid gas-permeable contact lenses and also in both eyes of one patient who discontinued contact lens wear. All seven eyes of five patients who declined refitting showed persistence or increase of pannus. The mean Dk/Lp of the hydrogel contact lenses for six eyes with pannus was 3.8 X 10(-9) cm ml O2/s ml mm Hg; mean Dk/Lp was 8.6 X 10(-9) cm ml O2/s ml mm Hg for the lens of the control eyes. This difference was found to be statistically significant (P = .028). CONCLUSIONS Peripheral, contact lens-induced hypoxia is a risk factor for corneal pannus, and conversion from hydrogel or polymethylmethacrylate contact lenses to daily wear rigid gas-permeable contact lenses in these eyes successfully reversed this complication.