Our aim was to clarify whether substitution of cytosine for adenine at position 1166 (A1166C) polymorphism of the angiotensin II type 1 receptor (AT1R) gene is associated with susceptibility to essential hypertension in Han, Tibetan and Yi populations in China. This study involved 302 normotensive and 446 hypertensive subjects. The polymorphism was detected by polymelase chain reaction of genomic DNA and restriction fragment length polymorphism (PCR-RFLP) in genomic DNA. The data were analyzed by analysis of covariance (ANCOVA), X2 test, and multiple logistic regression. In normotensive controls, the A1166 allele frequencies were 0.979, 0.939 and 0.965 in Han, Tibetan and Yi participants, respectively. There was no significant intergroup variation in frequency of the allele in normotensives (X2=4.166, p=0.125). The frequency of the A1166 allele was significantly higher in Tibetan male hypertensives than that in normotensives (X2=11.46, p=0.001). There was no significant difference in A1166C genotype distribution and allele frequency between normotensives and hypertensives either in the Han (p=0.465) or Yi (p=0.357) populations. Body mass index in the Han and Yi populations (p=0.0001), age in the Tibetan and Yi populations (p=0.0001), and AA genotype in the Tibetan male population (p=0.0034) all were independent risk factors for hypertension. Diastolic blood pressure levels were significantly higher in Tibetan male subjects with the AA genotype than in those with the AC+CC genotype (p=0.0040). We concluded that the A1166 allele is very common in Han, Tibetan and Yi populations, approximately 1.35-fold more common than in Caucasians. The A1166 allele of the AT1R gene may be a predisposing factor for essential hypertension in Tibetan males. A1166C polymorphism of the AT1R gene is probably not involved in the pathogenesis of essential hypertension in Han or Yi populations.