PURPOSE: Febrile seizure (FS) is the most common type of seizure. The role of genetic factors in FSs has long been recognized. A positive family history can be elicited in 25-40% of patients with FSs; nonetheless, the genes responsible for FSs in the majority of the population remain unknown. Interleukin-1beta (IL-1beta) is a pro-inflammatory cytokine that acts as an endogenous pyrogen. Thus, IL-1beta could be involved in the pathophysiology of FSs. METHODS: To determine whether or not single nucleotide polymorphisms of the IL-1beta gene are associated with susceptibility to simple FSs, IL-1beta promoter -31 and -511 genotyping was performed by means of polymerase chain reaction-restriction fragment (PCR-RF) length polymorphism in 40 FS patients (20 sporadic and 20 familial FS patients) and 33 controls. RESULTS: There were no significant differences in the frequencies of -31 C/T and -511 C/T in the IL-1beta promoter gene, between simple FS patients and controls. CONCLUSION: The frequency of CT/CT increased relatively in familial FS patients. A study examining a larger number of FS patients is needed.