Increased social and economic integration across the US-Mexican borders has led to important new developments in public health. Lower levels of cardiovascular mortality have been observed among Mexican Americans (MAs) although few direct comparisons have been undertaken with Mexico. Using survey data in the respective countries we examined blood pressure (BP) levels, hypertension prevalence and patterns of awareness, treatment and control in Mexico and among MAs. A national representative sample of the adult population from Mexico collected in 2000 (N=49 294), and data on 8688 MA participants in the 1999-2004 National Health and Nutrition Examination survey from the United States were available for analysis. US-born MAs and those born in Mexico were analysed separately in the US data. Lack of direct standardization of methods between surveys necessitated statistical adjustment of BP values. Analyses were based on persons aged 25-64 in each country. Sex- and age-adjusted mean systolic/diastolic BPs were 122/80, 119/71 and 120/73 in Mexicans, immigrant MAs and US-born MAs, respectively. The prevalences of hypertension (BP > or = 140/90 or treatment) were 33, 17 and 22%. Hypertension control rates were 3.7, 32.1 and 37.9%, in the same groups. Awareness and treatment rates were 25 and 13% in Mexico and 54 and 46% among MAs in the United States, respectively. Hypertension appears to be more common in Mexico than among Mexican immigrants to the United States. Despite relatively low access to health insurance in the United States, hypertension control increased over the course of this migration.