Background: Women with chronic hypertension who become pregnant have an increased risk of preeclampsia and adverse neonatal outcomes. However, within this group, the risk factors for these adverse events are not known. Methods: We analyzed data on outcomes for 763 women with chronic hypertension enrolled in a multicenter trial of low-dose aspirin for the prevention of preeclampsia. Preeclampsia was defined as new-onset proteinuria (urinary protein excretion, ≤300 mg per 24 hours) in the 682 women without proteinuria at base line. It was defined according to strict clinical criteria in the 81 women who had proteinuria at base line. The end points were maternal and neonatal outcomes. Results: Among the 763 women, 193 (25 percent) had preeclampsia. The frequency of preeclampsia was not affected by the presence of proteinuria at base line (27 percent among women with proteinuria, vs. 25 percent among those without it), but it was greater in women who had had hypertension for at least four years (31 percent vs. 22 percent; odds ratio, 1.6; 95 percent confidence interval, 1.1 to 2.2) and in those with preeclampsia during a previous pregnancy (32 percent vs. 23 percent; odds ratio, 1.6; 95 percent confidence interval, 1.1 to 2.3). Women with proteinuria at base line were significantly more likely to deliver their babies at less than 35 weeks of gestation (36 percent vs. 16 percent; odds ratio, 3.1; 95 percent confidence interval, 1.8 to 5.3) and to have infants that were small for gestational age (23 percent vs. 10 percent; odds ratio, 2.8; 95 percent confidence interval, 1.6 to 5.0). Conclusions: In women with chronic hypertension, the presence of proteinuria early in pregnancy is associated with adverse neonatal outcomes independently of the development of preeclampsia.