Objective To determine the interleukin(IL)-17 concentrations in serum and synovi-al fluid from patients with knee osteoarthritis(OA),and evaluate their correlation with disease severity. Methods Serum and synovial fluid were collected from 100 patients with primary knee OA;age-and sex-matched 50 healthy subjects provided serum samples as controls.OA severity and grade were assessed u-sing the Lequesne index and Kellgren and Lawrence(K-L)grading system,respectively.The expression of IL-17 was quantified by enzyme-linked immunosorbent assay.Results Serum IL-17 concentrations were significantly higher in patients than in controls(P <0.05).In the patient group,patients with K-L grade 3 and 4 had higher synovial IL-17 levels than those with K-L grade 2(P <0.05).At the same time,com-pared with K-L grade 3,there was a higher IL-17 level in K-L grade 4 patients(P <0.05).Synovial fluid IL-17 concentration was positively correlated with Lequesne index(r =0.6232,P <0.05).There was no correlation between serum IL-17 concentrations and Lequesne index,however.Conclusion The expres-sion of IL-17 was significantly increased in serum and synovial fluid of knee from patients with knee OA. There was a positive correlation between synovial fluid IL-17 concentrations and OA severity.It suggests that the imbalance of IL-17 expression plays a certain role in the pathogenesis of OA.