Despite strong linkage of ankylosing spondylitis (AS) with human leukocyte antigen (HLA) B27, its contribution to disease susceptibility is only 15%, and additional genetic factors are likely to be involved in AS. Interleukin (IL)-1 locus has been linked to AS in European population. Thus, we studied IL-1 receptor antagonist polymorphism in Indian patients with AS. One hundred and sixty-two patients with AS and ethnically matched healthy controls were included. IL-1Ra variable number tandem repeat polymorphism was studied by polymerase chain reaction (PCR). HLA B27 was done by amplification refractory mutation system PCR. Clinical details regarding severity of articular disease, presence of peripheral arthritis, and extra-articular manifestations were collected. The mean age of these 162 patients was 35 years, and the mean duration of disease was 10.8 years. Of these 162 patients, 137 were HLA B27 positive. The commoner alleles--IL-1RN*1 and IL-1RN*2--together accounted for 99.5% of the IL-1RN alleles in the control population and 98.5% of the cases. The allele frequency as well as the carriage rate of allele IL-1RN*2 were significantly higher in patients with AS than the control populations (26.3 vs 16.2% and 41.97 vs 22.5%, respectively; p=0.015 and 0.0002). The IL-1RN*2 allele was not associated with any difference in clinical disease expression. The IL-1RN*2 allele is a susceptibility marker for AS in the Indian population but does not influence disease phenotype.