Abstract: Introduction: There are several reports of good effects of Cyclosporine A (CsA) in the treatment of Behcet's disease (BD). We studied the long term effect of CsA in prospective open clinical trial on posterior uveitis (PU) and retinal vasculitis (RV) of BD. Materials & Methods: Twenty three patients with PU and/or RV diagnosed as BD (according to the Iran and to the Japan criteria) were selected. Initially CsA 5 mg/Kg/day orally in addition to Prednisolone 0.5 mg/Kg/day was administered. A disease activity index (DAI) based on the inflammatory state of each section of each eye, visual acuity (VA) and a total adjusted DAI for each patient was calculated. The comparison of these data before and after the treatment was made by the student paired t test. Results: Nineteen patients completed the study with a mean follow up time of 25.1 months. PU improved in 85% of the eyes; the mean DAI decreased from 2.1 to 0.6 (p=0.000004). RV improved in 50% of the eyes; the mean DAI decreased from 1.6 to 1 (p=0.18). VA improved in 57% of the eyes; the mean VA improved from 3.2 to 5.4 on 10 by the Snellen chart (p=0.02). The total adjusted DAI, improved in 74% of the patients. The mean total adjusted DAI decreased from 35.2 to 21 (p<0.002). Adverse effects were seen in 90% of the patients, but all were reversible with the adjustment of the dose, and no permanent abnormality was seen. Conclusion: This study demonstrates the beneficial effect of CsA in severe ocular lesions of BD. The efficacy is comparable to cytotoxic drugs (such as pulse Cyclophosphamide, Methotrexate, Chlorambucil and etc.). There is no limitation in the long-term use of the drug. as the adjustment of the dose produced no permanent abnormality. CsA may be considered as one of the major drugs in resistant cases.