Background Nitric oxide (NO) synthesized by endothelial nitric oxide synthase (eNOS) plays an important role in both the regulation of endothelial function and the control of blood pressure. Up to now, there has been conflicting data regarding the association between three clinically relevant polymorphisms (T-786C, intron4b/a and G894T) of the eNOS gene and essential hypertension. Methods To examine the contribution of the three eNOS gene polymorphisms to the development of hypertension in the northern Han Chinese, a case-control study including 503 hypertensive cases and 490 age-, gender-, and area-matched controls recruited from the International Collaborative Study of Cardiovascular Disease in Asia (InterASIA) was conducted. Genotyping was performed by polymerase chain reaction (PCR) or PCR-restriction fragment length polymorphism (RFLP). Results The T-786C and intron4b/a polymorphisms were observed in significant linkage disequilibrium (D’=0.87, P<0.001). The minor allele frequencies of these three polymorphisms in healthy controls were much lower than those of Caucasians (9.3% vs 39.6%-42.0%, 8.9% vs 15.0% -16.0% and 10.9% vs 34.5%-34.9% for -786C, intron4a and 894T, respectively). Genotype distributions and allele frequencies of the three polymorphisms did not differ between cases and controls (all P > 0.05). In addition, none of the eight estimated haplotypes significantly increased or decreased the risk of hypertension before or after adjustment for several known risk factors. Conclusion The study results suggest that the three eNOS gene polymorphisms are unlikely to be major genetic susceptibility factors for essential hypertension in the northern Han Chinese population. Background Nitric oxide (NO) synthesized by endothelial nitric oxide synthase (eNOS) plays an important role in both the regulation of endothelial function and the control of blood pressure. Up to now, there has been conflicting data regarding the association between three clinically relevant polymorphisms (T-786C, intron4b / a and G894T) of the eNOS gene and essential hypertension. Methods To examine the contribution of the three eNOS gene polymorphisms to the development of hypertension in the northern Han Chinese, a case-control study including 503 hypertensive cases and 490 age-, gender-, and area-matched controls recruited from the International Collaborative Study of Cardiovascular Disease in Asia (InterAIA) was conducted. Genotyping was performed by polymerase chain reaction (PCR) or PCR- restriction fragment length polymorphism (RFLP) . Results The T-786C and intron4b / a polymorphisms were observed in significant linkage disequilibrium (D ’= 0.87, P <0.001). The minor allele frequenci es of these three polymorphisms in healthy controls were much lower than those of Caucasians (9.3% vs 39.6% -42.0%, 8.9% vs 15.0% -16.0% and 10.9% vs 34.5% -34.9% for-786C, intron4a and 894T, respectively). Genotype distributions and allele frequencies of the three polymorphisms did not differ between cases and controls (all P> 0.05). In addition, none of the eight estimated haplotypes significantly increased or decreased the risk of hypertension before or after adjustment for several known risk factors. Conclusion The study results suggest that the three eNOS gene polymorphisms are unlikely to be major genetic susceptibility factors for essential hypertension in the northern Han Chinese population.