The side-effects of long-term cyclosporin A (CyA) treatment in 26 patients with severe psoriasis were evaluated. These patients had a mean PASI score of 30.2 and were treated with CyA for between 7 and 37 months (mean 19.5 months). There were three groups according to the dose of CyA, less than 2 mg/kg per day, 2-3 mg/kg per day and greater than 3 mg/kg per day. In all three groups, CyA was found to be equally effective. Treatment with CyA was discontinued in 12 of the 26 patients because of nephrotoxicity and/or development of hypertension. One was in the less than 2 mg/kg per day group, three were in the 2-3 mg/kg per day group and eight in the greater than 3 mg/kg per day group. There was no hepatotoxicity with CyA treatment. One patient developed two squamous cell carcinomas of the skin.