Exposure to Escherichia coli O157:H7 may result in subclinical kidney injury manifesting as hypertension during pregnancy. We evaluated the risk of pregnancy-related hypertension (PRH) among previously healthy females from the Walkerton Health Study, Canada (2002-6), who conceived within five years of exposure to bacteria-contaminated drinking water. Ontario Ministry of Health Antenatal forms were used to determine outcomes and risk factors. PRH was defined as any systolic or diastolic blood pressure (BP) > or =140 mm Hg and > or =90 mm Hg, respectively. Chronic and gestational hypertension were defined, respectively, as elevated BP observed prior to or at > or =20 weeks gestation. Risk of PRH was evaluated using a modified Poisson regression model that controlled for known risk factors. Of 148 eligible pregnancies, antenatal audits with blood pressure data were available for 135. PRH was detected in 20.7% pregnancies, of which 6.7% were chronic hypertension and 14.1% gestational hypertension. Although nonsignificant, we observed a consistent trend toward higher rates of PRH and mean arterial pressure, particularly prior to 20 weeks gestation, among women who reported symptomatic gastroenteritis compared to asymptomatic women. BP should be monitored closely in women after exposure to contaminated water.