Aim of the work: To investigate serum and synovial fluid levels of IL-17 in rheumatoid arthritis (RA) patients, and its correlation with disease activity and severity. Patients and methods: 20 RA patients together with 20 primary knee osteoarthritis (KOA) patients and 15 healthy individuals matched for age and sex as control groups were enrolled in this study. Both RA and KOA patients presented with knee effusion. Paired samples of serum and synovial fluid (SF) were collected from RA, OA patients and serum samples from the healthy individuals. RA disease activity was assessed using DAS-28 score and power Doppler ultrasound (PDUS) according to the European League against Rheumatism (EULAR). Radiographic damage was evaluated according to Larsen score. Results: Serum levels of IL-17 were significantly elevated in RA patients compared to controls (p < 0.001). Also, SF of IL-17 was significantly higher in RA patients compared to OA patients (p < 0.001). In addition, synovial level of IL-17 was significantly higher in RA patient compared to their serum level (p < 0.001). Regarding disease activity grading among RA patients, significant differences (p < 0.05) in mean serum and synovial IL-17 levels were reported being higher in severe active disease. Positive correlations of serum and SF IL 17 levels with PDUS findings and Larsen score were reported. Conclusion: Serum and synovial IL-17 levels were significantly elevated in RA patients which clarifies its possible role in RA pathogenesis and correlates positively with disease activity parameters, PDUS findings and Larsen score. Thus targeting IL-17 may provide a promising role in suppressing RA.