Obesity is an important risk factor for hypertensive disorders of pregnancy, but most cases of hypertensive disorders of pregnancy occur in women of normal weight. There may be predisposing factors to both hypertensive disorders of pregnancy and obesity. To test this hypothesis, the authors compared changes in body mass index (weight (kg)/height (m)2) over time in women with and without hypertensive disorders of pregnancy. They used data from 3,572 women who received antenatal care at a major public hospital in Brisbane, Australia, between 1981 and 1984 and who were followed up for 21 years. A total of 318 women (8.9%) had experienced hypertensive disorders in the index pregnancy, and 233 of them (73.3%) had a baseline body mass index of <or=25 kg/m2. After the authors adjusted for all potential confounding factors, they found that women with hypertensive disorders of pregnancy gained on average 1.35 kg/m2 more (95% confidence interval: 0.80 kg/m2, 1.89 kg/m2) in body mass index over 21 years than women without hypertensive disorders of pregnancy. The odds of gaining>or=5 kg/m2 were 59% greater for women who experienced hypertensive disorders of pregnancy compared with those who did not (odds ratio=1.59, 95% confidence interval: 1.24, 2.04). The authors concluded that hypertensive disorders of pregnancy are associated with increased weight gain over 21 years.