In adipose tissue metabolism, cytokines were major regulators. mRNA expression studies show that adipocytes can synthesize both tumor necrosis factor-alpha and several interleukins (ILs), notably IL-1 beta (IL-1beta) and IL-6. In particular, IL-1beta expression is under strong genetic control. We examined the relationship among obesity, polymorphism of the IL-1beta at position +3953 in exon 5, and Sasang constitution. In a group of 181 healthy females with a marked variation in body mass index (BMI), we determined the genotype of IL-1beta by polymerase chain reaction-restriction fragment length polymorphism assays. A significant decrease was found for the IL-1beta T allele in the overweight group (BMI 25 approximately 29 kg/m(2)) compared with the lean group with a BMI < 25 kg/m(2) (P = .049, odds ratio [OR] = 0.296). Carriers of T allele in the heterozygous or homozygous form did not show a significant difference in physical and clinical characteristics. In addition, in Taeumin female subjects, the frequency of IL-1beta T allele was apparently decreased in the overweight group (BMI 25 approximately 29 kg/m(2)) compared with the lean group with a BMI < 25 kg/m(2) (P = .007, OR = 0.152). In overweight women, we found an association between the +3953 C/T polymorphism in the IL-1beta gene and BMI. In addition, we found an association among IL-1beta polymorphism, obesity, and Sasang constitution.