To quantify the risk for age-related cortical cataract and posterior subcapsu lar cataract (PSC) associated with having an affected sibling after adjusting fo r known environmental and personal risk factors. Sibling cohort study. Participa nts in the ongoing Salisbury Eye Evaluation (SEE) study (m=321; mean age, 78.1± 4.2 years) and their locally resident siblings (m=453; mean age, 72.6±7.4 years ) were recruited at the time of Rounds 3 and 4 of the SEE study. Retroilluminati on photographs of the lens were graded for the presence of cortical cataract and PSC with the Wilmer grading system. The residual correlation between siblings’ cataract grades was estimated after adjustment for a number of factors (age; gen der; race; lifetime exposure to ultraviolet-B light; cigarette, alcohol, estrog en, and steroid use; serum antioxidants; history of diabetes; blood pressure; an d body mass index) suspected to be associated with the presence of cataract. The average sibship size was 2.7 per family. Multivariate analysis revealed the mag nitude of heritability (h2) for cortical cataract to be 24%(95%CI, 6%-42%), whereas that for PSC was not statistically significant (h2 4%; 95%CI, 0%-11 %) after adjustment for the covariates. The model revealed that increasing age, female gender, a history of diabetes, and black race increased the odds of cort ical cataract, whereas higher levels of provitamin A were protective. A history of diabetes and steroid use increased the odds for PSC. This study is consistent with a significant genetic effect for age-related cortical cataract but not PS C. To quantify the risk for age-related cortical cataract and posterior subcapsu lar cataract (PSC) associated with having an affected sibling after adjusting fo r known environmental and personal risk factors. Sibling cohort study. Participation in the ongoing Salisbury Eye Evaluation (SEE) The average age (78.1 ± 4.2 years) and their locally resident siblings (m = 453; mean age, 72.6 ± 7.4 years) were recruited at the time of Rounds 3 and 4 of the SEE study. Retroilluminati on photographs of the lens were graded for the presence of cortical cataract and PSC with the Wilmer grading system. The residual correlation between siblings’ cataract grades was estimated after adjustment for a number of factors (age; gen der; race; lifetime exposure to ultraviolet-B light; cigarette, alcohol, estrog en, and steroid use; serum antioxidants; history of diabetes; blood pressure; an d body mass index) suspected to be associated with the presence of cataract. The average sibship size was 2.7 per Multivariate analysis revealed the magitude of heritability (h2) for cataract cataract to be 24% (95% CI, 6% -42%), but that for PSC was not quite significant (h2 4%; 95% CI, 0 % -11%) after adjustment for the covariates. The model revealed that increasing age, female gender, a history of diabetes, and black race increased the odds of cortical cataract, yet higher levels of provitamin A were protective. A history of diabetes This study is consistent with a significant genetic effect for age-related cortical cataract but not PS C.