We studied prospectively the weight change and the effect of weight change on changes in coronary heart disease risk factors in a population-based sample of 485 middle-aged women. All women were studied first in 1983 to 1984, when they were premenopausal and aged 42 to 50 years, and then restudied in 1987. Women gained an average of 2.25 +/- 4.19 kg during this 3-year period; 20% of women gained 4.5 kg or more, and only 3% lost 4.5 kg or more. There were no significant differences in weight gain of women who remained premenopausal and those who had a natural menopause (+2.07 kg vs +1.35 kg). Weight gain was significantly associated with increases in blood pressure and levels of total cholesterol, low-density lipoprotein cholesterol, triglycerides, and fasting insulin. Weight gain is thus a common occurrence for women at the time of menopause and is related to the changes in coronary heart disease risk factors observed during this period. Efforts to lose weight or to prevent weight gain may help to mitigate the worsening in coronary heart disease risk factors in middle-aged women.