To determine the possible role of glucose and lipid metabolism in the formation of cataract in elderly people we studied 463 patients undergoing cataract extraction. Of 188 males, 35 (19%) had posterior subcapsular cataract (group 1), 27 (14%) had cortical cataract (group 2), and 24 (13%) had nuclear cataract (group 3). Of 275 females, 27 (10%) belonged to group 1, 44 (16%) to group 2, and 33 (12%) to group 3. Patients in group 1 were significantly younger than those of group 2 and 3. In addition, patients in group 1 had higher concentrations of fasting serum triglycerides than patients of group 2 or 3. No difference in mean concentrations of serum cholesterol was observed between the different groups. However, fasting plasma glucose concentrations were higher in group 1 patients than in those of group 2 or 3. Patients in group 1 had a higher 'Broca index' than those in group 2 or 3, with the exception of males in group 3. These results suggest that the association of hypertriglyceridemia, hyperglycemia and obesity favors the formation of a specific morphologic type of lens opacity, posterior subcapsular cataract, occurring at an early age. They imply the possibility of effective modes of preventive therapy for a subgroup of patients with 'senile' cataract.