As there is a high prevalence of obesity in Tonga, we aimed to determine the distribution of the ��2 adrenoceptor gene Gln27Glu polymorphism and to assess its relevance to obesity and to Type II diabetes, known to be prevalent in that population. A random sample of 1022 individuals from Tonga were genotyped for the Gln27Glu polymorphism in the ��2 adrenoceptor gene. To assess the prevalence of obesity we measured body-mass index (BMI), fat-free mass, percentage fat and waist-to-hip ratio (WHR). To assess glucose metabolism we measured HbAlc, fasting blood glucose, fasting serum insulin, and 1- and 2-h glucose; we also measured serum lipid and creatinine levels. We found that 84% of the Tongan men and 93% of the women were overweight or obese (BMI ��� 25 kg/m2) and 15.1% had Type II diabetes. Genotype frequencies among the 1022 Tongans were: Gln/Gln 90.3% and Gln/Glu 9.6%; we found one Glu/Glu homozygote. The mean BMI (��S.D.) for men was not significantly different for those who were homozygous (30.2��5.4 kg/m2) or heterozygous (30.1��5.5 kg/m2) for the Gln allele; this was also true for women (33.7��6.2 kg/m2 for homozygous and 34.0��5.6 kg/m2 for heterozygous). The Glu allele was not associated with other measures of obesity or abnormal glucose metabolism in this generally overweight population. There is a unique frequency of the Gln/Glu ��2 adrenoceptor polymorphism among Tongans. We found no association of the polymorphism with obesity measures or Type II diabetes-related variables in the Tongan population among whom we documented a high prevalence of obesity and Type II diabetes and a low frequency of the Glu allele.