Exposure to mercury has been linked to elevations in blood pressure (BP), though few data are available. We examined the cross-sectional relationship between blood mercury concentration and BP in a representative US sample of 1240 women, aged 16–49 years, from the National Health and Nutrition Examination Survey 1999–2000. We found no association overall between mercury and BP in multivariate models. We stratified our data by dietary fish intake (presumably reflecting the consumption of long-chain n-3 fatty acids that may reduce BP) resulting in 759 fish consumers and 481 non-fish consumers. We found that for each 1.3 μg/L (interquartile distance) increase in mercury, systolic BP significantly increased by 1.83 mm Hg (95% CI: 0.36, 3.30) among non-fish consumers. A similar pattern was seen for diastolic BP, although it was non-significant. While an adverse effect of mercury exposure at background levels on BP was not present overall, an adverse association was present among non-fish-consuming young and middle-aged women.