Interleukin-33 (IL-33) is a novel alarmin that warns immune cells of tissue destruction in injury or infection.This study is aimed at analyzing and correlating the concentration of IL-33 in the gingival crevicular fluid (GCF) and plasma of healthy subjects and chronic and aggressive periodontitis patients with intronic variant single nucleotide polymorphisms (SNPs), rs1157505 (C/G) and rs7044343 (C/T) in the IL-33 gene.This is a cross-sectional, biochemical, genetic study.Ninety subjects were divided into Group H: subjects with healthy periodontium, Group CP: chronic periodontitis patients, and Group GAgP: generalized aggressive periodontitis patients, based on clinical parameters of periodontal inflammation. IL-33 concentration in GCF, as well as plasma, was quantified using enzyme-linked immunosorbent assay. The SNPs rs1157505 and rs7044343 were analyzed using polymerase chain reaction-restriction fragment length polymorphism.A significant difference was found in IL-33 concentration in GCF and plasma between the three groups. GG genotype of IL-33 SNP rs1157505 was associated with the highest GCF and plasma IL-33 concentration and was significantly more in GAgP than healthy or CP groups. IL-33 SNP rs7044343 did not show any such association. All GAgP patients had the highest GCF and plasma concentration of IL-33.IL-33 may be a potential inflammatory marker of periodontitis. GG genotype of SNP rs1157505 may be associated with GAgP.