OBJECTIVE: To investigate the correlation between interleukin-1ß (IL-1ß), interleukin-1 receptor antagonist (IL-1ra) and the obesity of polycystic ovary syndrome (PCOS). METHODS: (1) From Oct. 2006 to Jan. 2007, 118 PCOS patients were enrolled in this study in Peking University Third Hospital, which were divided into 56 patients in obese PCOS group and 62 patients in non-obese PCOS group according to the WHO International Obesity Task Force Asia-Pacific criteria [body mass index (BMI) 25 kg/m(2)]. The polymorphism of IL-1ß gene promoter region, exon-5 and intron 2 of IL-1ra gene were detected by PCR. (2) Twenty-nine obese PCOS patients and 31 non-obese PCOS patients were selected randomizedly serum levels of IL-1ß, IL-1ra were measured by ELISA, in the mean time, serum levels of fasting glucose, fasting insulin and the total white blood cell, hypersensitive C-reactive protein levels were measured. RESULTS: (1) Genetic test:the frequency of TT genotype and T allele of IL-1ß promoter region (-511) in obese PCOS patients were significantly higher than those in non-obese patients (44.6% vs. 11.3%, 63.4% vs. 39.5%, all P < 0.05). The frequency of IL-1raI/V genotype and V allele of IL-1ra gene were 19.6% and 9.8% in obese PCOS patients, which were significantly higher than those in non-obese group (3.2% and 1.6%, P < 0.05). (2) Serological test:serum level of IL-1ß and IL-1ra of (149 ± 36) and (284 ± 97) ng/L in obese PCOS group which were significantly higher than those in non-obese PCOS group [(96 ± 42) and (208 ± 84) ng/L, P < 0.05]. Fasting blood glucose, fasting insulin and hypersensitive C-reactive protein and white blood cell count were (5.1 ± 0.7) mmol/L, (17 ± 9) mU/L, (1.5 ± 0.6) mg/L and (7.0 ± 2.3) × 10(9)/L in obese PCOS group, which were significantly higher than in non-obese PCOS group [(4.9 ± 0.5) mmol/L, (11 ± 8) mU/L, (0.9 ± 0.4) mg/L and (5.9 ± 1.3) × 10(9)/L, P < 0.05]. (3)The correlation between interleukin and BMI: serum levels of IL-1ß (r = 0.673) and IL-1ra (r = 0.557) were positively correlated with BMI in PCOS patients (P < 0.05). CONCLUSIONS: Inflammatory factors IL-1ß and IL-1ra had correlation with obesity of PCOS patients, PCOS patients who carried T allele of IL-1ß gene promoter region (-511) and V allele of IL-1ra gene were high risk of obesity.