Obesity and inflammation are known to correlate with the pathogenesis of obstructive sleep apnea syndrome (OSAS). Interleukin (IL)-6, an important regulator of obesity and inflammation, was reported to phenotypically increase in patients with OSAS. This study aimed to investigate whether genetic variants in IL-6 confer susceptibility to OSAS. The study population consisted of 151 patients with OSAS and 75 healthy controls from Southeast China. Five haplotype-tagging single nucleotide polymorphisms (tSNPs) were selected across 21 kb of the IL-6 locus using Haploview software V4.1. The tSNPs were amplified by polymerase chain reaction (PCR) and genotyped by restriction enzyme digestion followed by gel electrophoresis. Linkage disequilibrium (LD) and haplotype reconstruction were carried out by means of a SHEsis program. No distribution difference of any of the five tSNPs between OSAS patients and controls was observed. However, in non-obese individuals (n=117), the minor allele G (rs1800796) decreased risk of OSAS compared with the major allele C [odds ratio (OR), 0.48; 95% confidence interval (CI), 0.26-0.86; p=0.014], and the haplotype TG (rs1880242, rs1800796) conferred a significantly decreased risk of OSAS than single allele G (rs1800796) (OR, 0.39; 95% CI, 0.20-0.74; p=0.003). Moreover, the severity of sleep-disordered breathing (measured by apnea hypopnea index) increased linearly in carriers of the C variant of IL-6 -572G/C polymorphism (14.3+/-5.1, 22.0+/-3.6 and 34.8+/-3.5 for GG, CG and CC, respectively; p=0.012). To the best of our knowledge, this is the first study to suggest that genetic variants in IL-6 could modify OSAS susceptibility. SNP genotyping of IL-6 is a potential strategy for detecting the risk of breathing disordered diseases in non-obese individuals.