Background: Cyclosporine (CS) is being successfully used for various skin diseases including psoriasis, atopic dermatitis, and chronic idiopathic urticaria. However, dermatologists have hesitated to use CSs in clinical practices due to possible adverse effects. Objective: The aim of this study is to investigate the adverse effects of CS for dermatological uses. Methods: We performed a retrospective study by including 1,335 patients with CS treatment. Results: From 1,335 patients, 208 (15.6%) showed adverse effects and obvious laboratory changes. Twenty five patients experienced either two or more adverse effects. Gastrointestinal (GI) symptoms were the most common side effects. Other side effects included hypercholesterolemia (2.2%), hypertrichosis (2.2%), headache (1.3%), hypertension (0.9%), and hypertriglyceridemia (0.9%). Hypercholesterolemia is more frequently found in men but, GI symptoms and hypertrichosis are more frequent in women. Hypercholesterolemia, hypertriglyceridemia, and GI symptoms are more common in adults but hypertrichosis is more common in children and adolescents. Hypertension, hypercholesterolemia, and hypertriglyceridemia have been remarkable in psoriasis patients, and GI symptoms and hypertrichosis are found in patients with atopic dermatitis. GI symptoms and headaches occur more often within three months of the CS treatment; however, hypertension, hypercholesterolemia, and hypertriglyceridemia usually occur three months after. With regards to CS dose, the hypertrichosis is more common in the group with low initial dose. GI symptoms occur more often in the lower CS cumulative dose group; however, hypertension and hypertriglyceridemia are higher in the CS cumulative dose group. Conclusion: As compared with previous studies, the frequency of adverse effects after CS treatment in this study is proved to be low. Therefore, under dermatological fields, we suggest that CS is a relatively safe drug with periodic follow-ups and laboratory tests. (Korean J Dermatol 2013;51(12):960∼969)