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 microg/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.