Context Outside of pregnancy, home blood pressure (BP) has been shown to be superior to office BP for predicting cardiovascular outcomes. Objective This work aimed to evaluate home BP as a predictor of preeclampsia in comparison with office BP in pregnant women with preexisting diabetes. Methods A prospective cohort study was conducted of 404 pregnant women with preexisting diabetes; home BP and office BP were measured in early (9 weeks) and late pregnancy (35 weeks). Discriminative performance of home BP and office BP for prediction of preeclampsia was assessed by area under the receiver operating characteristic curves (AUC). Results In total 12% (n = 49/404) developed preeclampsia. Both home BP and office BP in early pregnancy were positively associated with the development of preeclampsia (adjusted odds ratio (95% CI) per 5 mm Hg, systolic/diastolic): home BP 1.43 (1.21-1.70)/1.74 (1.34-2.25) and office BP 1.22 (1.06-1.40)/1.52 (1.23-1.87). The discriminative performance for prediction of preeclampsia was similar for early-pregnancy home BP and office BP (systolic, AUC 69.3 [61.3-77.2] vs 64.1 [55.5-72.8]; P = .21 and diastolic, AUC 68.6 [60.2-77.0] vs 66.6 [58.2-75.1]; P = .64). Similar results were seen when comparing AUCs in late pregnancy (n = 304). In early and late pregnancy home BP was lower than office BP (early pregnancy P < .0001 and late pregnancy P < .01 for both systolic and diastolic BP), and the difference was greater with increasing office BP. Conclusion In women with preexisting diabetes, home BP and office BP were positively associated with the development of preeclampsia, and for the prediction of preeclampsia home BP and office BP were comparable.