Persons with diabetes mellitus have been found to be at increased risk of developing cataracts when compared with nondiabetic persons. This report describes the study of characteristics which may be related to this problem in a population-based sample of diabetic persons. Prevalence of surgical aphakia and cataract increased with increasing age in both younger and older onset diabetic persons. Females had higher rates than males. In multivariate analyses, for younger onset persons, longer duration of diabetes, older age at examination, increased severity of retinopathy, diuretic usage and higher glycosylated hemoglobin levels were significantly associated with greater prevalence of cataract. In older onset persons, age at examination, increased severity of retinopathy, diuretic usage, lower intraocular pressure, smoking and lower diastolic blood pressure were significantly associated with greater prevalence of cataract. Longitudinal data concerning the relationship of some of these characteristics to subsequent development or progression of cataract are necessary before considering the possibility of preventive trials in this condition.