The aim of this study was to evaluate the association of polymorphism in IL-1 receptor antagonist (IL-1RA) gene intron 2 with susceptibility to rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) and their clinical features. Polymerase chain reaction of a genomic DNA was used to determine genotypes of the IL-1RA in 138 RA, 93 SLE, and 127 healthy control subjects. The frequency of IL-1RA allele 2 (IL-1RN*2) was lower in RA patients (2.5%) than in control subjects (7.1%) (odds ratio 0.34, 95% confidence interval 0.13-0.88, P=0.02). There was a significant difference in genotype and allele distribution between RA patients and controls. However, it did not differ between SLE patients and controls. In SLE and RA patients, there was no significant difference in clinical and laboratory findings concerning IL-1RA polymorphisms. In conclusion, our data suggest that IL-1RA gene polymorphism is not responsible for specific clinical characteristics in RA and SLE but that IL-1RN*2 is relevant in the susceptibility to RA, suggesting a protective role of IL-1RN*2 in the pathogenesis of RA.