In this study, we investigated the association between RA and single-nucleotide polymorphisms (SNPs) of co-stimulatory or co-inhibitory molecules in 124 RA cases and 100 healthy controls without immune-related diseases [including tumor necrosis factor superfamily member 4 (TNFSF4), CD28, cytotoxic T-lymphocyte–associated protein 4 (CTLA4), and programmed cell death protein 1 (PDCD1)]. The gene discussed is TNFSF4; the disease is rheumatoid arthritis.