Abstract Serum triglyceride concentration was measured by direct glycerol determination in 99 women, aged 17 to 90. The arithmetic mean level was 86 mg. per 100 ml. The lognormal mean was 77 mg. per 100 ml. A highly significant increase in circulating triglycerides was observed in women over age 35 compared to younger women (88 mg. and 53 mg. per 100 ml., respectively). Triglyceride levels were significantly higher in women who gained weight (101 mg. per 100 ml.) than in women with stable weight (75 mg. per 100 ml.). Higher triglyceride values in menopausal women (102 mg. per 100 ml.) compared to premenopausal women (75 mg. per 100 ml.) were of borderline statistical significance. Serum cholesterol and phospholipids were significantly higher in older women. Weight gain did not influence serum cholesterol levels. Alterations observed in lipoprotein distribution included a relative decrease in alpha-lipoprotein in women who gained weight. Free fatty acid levels did not vary with age. The most striking alteration in triglyceride concentration was the increment associated with aging. This influence prevailed independently of weight gain or cessation of ovarian function, which also contributed an increase. These observations may be related to the incidence of atherosclerosis.