Previous studies suggested that genetic polymorphisms in interferon regulatory factor 5 (IRF-5) are implicated in the susceptibility to a range of autoimmune diseases, including rheumatoid arthritis, systemic lupus erythematosus, and inflammatory bowel disease. Recently, IRF-5 has been implicated in inflammatory processes that are associated with excessive remodeling and atherosclerosis. Our purpose was to investigate the association between the IRF-5 polymorphisms and the risk of acute coronary syndrome (ACS) in a Chinese population. The 5 bp indel (insertion/deletion) (CGGGG) polymorphism, located 64 bp upstream of the alternative exon 1a of IRF-5 gene, and the deletion of 30 bp in exon 6 of IRF-5 gene were analyzed among 148 patients with ACS and 246 controls in a Chinese population, using a polymerase chain reaction-restriction fragment length polymorphism strategy and direct sequencing. The frequencies of (CGGGG)(3)(CGGGG)(4) genotype and (CGGGG)(4) allele in ACS patients were significantly higher than those in control subjects (p = 0.018, odds ratio [OR] = 1.76, 95% confidence interval [CI]: 1.10-2.81; p = 0.028, OR = 1.62, 95% CI: 1.05-2.50, respectively). However, no significant relationship between the 30 bp exon 6 polymorphism of the IRF-5 gene and the risk of ACS was observed (p = 0.770, OR = 0.96, 95% CI: 0.72-1.28). The 5 bp indel (CGGGG) polymorphism of the IRF-5 gene may be associated with susceptibility to ACS.