Essential hypertension is a multifactorial disease, and has been shown to be associated with insulin resistance. The relationship between the genetic variation of the insulin receptor (INSR) gene and essential hypertension In Korean population was investigated by the Nsi 1 restriction fragment length polymorphism (RFLP) pattern of this gene. The observed genotype frequencies of INSR gene were not deviated from those expected for the Hardy-Weinberg equilibrium (HWE), but a significant association was observed between essential hypertension and N1 allele of Nsi 1 RFLP at the INSR gene ($X^2$-test; P<0.05). Moreover, the frequency of N1 allele was significantly different between normotensives and essential hypertensives in subgroups that were not obese ($X^2$-test; P<0.05). These data suggest that the Nsil RFLP of INSR gene may be a useful genetic marker for essential hypertension in Korean population.