BACKGROUND: Hypertensive disorders of pregnancy, including pregnancy-induced hypertension (PIH) and preeclampsia (PE), complicate 2-8% of pregnancies. Few studies have examined environmental risk factors in relation to these conditions. OBJECTIVES: Our goal was to examine whether pesticide exposure during pregnancy was associated with hypertensive disorders of pregnancy. METHODS: We analyzed self-reported data from 11,274 wives of farmers enrolled in the Agricultural Health Study (AHS) between 1993 and 1997. Using logistic regression models, we estimated the adjusted odds ratios (AORs) for PIH and PE associated with pesticide-related activities during the first trimester of pregnancy. RESULTS: First-trimester residential and agricultural activities with potential exposure to pesticides were associated with both PIH [residential AOR = 1.27; 95% confidence interval (CI), 1.02-1.60; agricultural AOR = 1.60; 95% CI, 1.05-2.45] and PE (residential AOR = 1.32; 95% CI, 1.02-1.70; agricultural AOR = 2.07; 95% CI, 1.34-3.21). CONCLUSIONS: Exposure to pesticides during pregnancy may increase the risk of hypertensive disorders of pregnancy. Laboratory research may provide insights into relationships between pesticide exposure and hypertensive diseases of pregnancy.