The insertion/deletion polymorphism (rs3783553 TTCA/-) in the 3' untranslated region of interleukin-1A (IL1A) has been studied intensively and has been shown to affect tumor risk. We studied the frequency of the IL1A gene polymorphism rs3783553 and evaluated its relationship with breast cancer (BC). A hospital-based case-control study comprising 228 patients with histologically confirmed BC and 241 healthy subjects was conducted. Polymerase chain reaction was used to detect the IL1A rs3783553 polymorphism. The ins/ins (ttca/ttca) genotype was significantly associated with a decreased risk of BC compared with the del/del (-/-) genotype (OR = 0.48, 95% CI = 0.27-0.85). Moreover, the ins (ttca) allele distribution between cases and controls was significantly different from the del (-) allele distribution (OR = 0.74, 95% CI = 0.57-0.96). Thus, the rs3783553 polymorphism is associated with a decreased incidence of breast cancer.