Purpose: To evaluate the efficacy, safety and tolerability of topical Cyclosporine A in the treatment of moderate to severe dry eye disease. Patients and Methods: Sixty four patients of dry eye disease were enrolled in this study and divided into two groups A & B. Cyclosporine A, ophthalmic emulsion in two concentrations 0.05% and o 1% was used for treatment of the two groups respectively twice daily for about 3 months. Schirmer's test, rose bengal staining, superficial punctate keratitis, lOP, visual acuity and ocular surface disease index "aSD1'" were recorded before and after treatment. Follow up period was continued for about 3 months after stoppage of the 3 months treatment, also for detecting any other adverse effects. I Results: Nearly all the tests, symptoms and signs of this disease were improved with the use of Cyclosporine A the most significant improvement was in rose bengal staining, superficial punctate keratitis and the sandy or gritty feeling . There was also decrease in the "OSDI" score indicating decrease in the effect of dry eye symptoms on the patients daily lives. There was no significant difference In dose -response relationship between the two groups, and no significant adverse effect was detected. Conclusion: Cyciosporine A in both concentrations was safe and well tolerated. It improved the ocular symptoms and signs of dry eye disease and so decreased the effect of this disease on the visually related functions.