Radiation cataractogenesis is an important consideration for radiotherapy patients and for astronauts. Data in the literature suggest that gender and/or estrogen may play a role in the incidence of age-related cataracts. However, few data exist on the effect of gender on radiation-induced cataractogenesis. We compared the incidence and rate of progression of cataracts induced by ionizing radiation in male and female Sprague-Dawley rats. Male rats were implanted with either an empty silastic capsule or a capsule containing 17-beta-estradiol. Ovary-intact female rats were implanted with empty capsules. All rats received a single dose of 10 Gy (60Co gamma rays) to the right eye only. Lens opacification was measured at 2-4-week intervals with a slit lamp. The incidence of radiation-induced cataracts was significantly increased in male rats compared to female rats (P=0.034). There was no difference in the rate of cataract progression between the three groups. Our data suggest there is a gender-related difference in radiation-induced cataractogenesis, but the increased incidence of radiation cataractogenesis in male rats compared to female rats cannot be attributed to estrogen levels, since there was no difference in cataract incidence between male rats implanted with empty capsules and those implanted with capsules containing 17-beta-estradiol.