Objective: The aim of this study is to investigate the relationship between serum ferritin levels and disease activity in patients with systemic lupus erythematosus (SLE). Methods: Serum ferritin levels of 72 SLE patients were measured. The SLE patients were subdivided into two groups according to SLE disease activity index (SLEDAI) as less than or equal to10 and greater than or equal to11. The results were compared with 31 patients with rheumatoid arthritis (RA). 36 patients among 72 with SLE were evaluated before and after treatment. Results: Serum levels of ferritin in SLE patients were higher than RA patients (p < 0,001). There was a significant difference in ferritin levels before and after treatment. The levels of ferritin in SLE were positively correlated with SLEDAI scores. Patients with SLEDAI scores ≥11 had significantly higher serum ferritin levels. Conclusion: Serum ferritin levels may be a useful marker of disease activity in SLE patients.