Interleukins are mediators of inflammation, immunity and cancer. Interleukin-15 (IL-15) is a cytokine produced by several leukocytes including phagocytes in response to infections and other signals that trigger innate immunity. Many studies suggested that IL-15 may play a primary role in the development of Rheumatoid Arthritis (RA), Juvenile Rheumatoid Arthritis (JRA) and Systemic Lupus Erythematosus (SLE). IL-15 is also implicated in the pathogenesis in other rheumatic diseases e.g. Scleroderma, Behcet's disease, Psoriasis, Polymyositis/ Dermatomyositis, Sarcoidosis, multiple sclerosis and inflammatory bowel disease .The aim of the current study is to determine serum levels of IL-15 in patients with RA, SLE, and Scleroderma (SSc) and to correlate these levels with different disease parameters. Patients and Methods: Sixty patients; (twenty RA patients, twenty SLE patients and twenty Scleroderma patients) and twenty age and sex- matched controls were included in the study. We investigated the serum level of the pro-inflammatory IL-15 in serum samples from patients and controls using the ELISA technique. Serum levels of IL-15 was correlated with various parameters of these diseases.Results: Serum level of IL-15 was higher in SLE and Scleroderma patients than the controls but lower in RA patients than the controls. These differences were of no statistical significance.Furthermore, serum level of IL-15 was correlated to different clinical and laboratory parameters of the diseases and to disease activity scores. Conclusion: Results reported in the current study as well as in the previous matching studies highlights the role of this novel cytokine IL-15 in patients with rheumatic diseases. IL-15 might be a potential pathogenic cytokine in different rheumatic diseases that correlates with different clinical and laboratory manifestations. IL-15 represents a potential target for future intervention.