We report a 9-year-old Icelandic male with Alport syndrome and nephrotic-range proteinuria who responded well to cyclosporine therapy. He presented at the age of 2 years with gross hematuria and proteinuria during an episode of upper respiratory tract infection. Three years later he had developed persistent proteinuria; kidney function was normal. A renal biopsy revealed marked irregularities in the glomerular basement membrane consistent with Alport syndrome. Mutation analysis revealed a single base insertion in COL4A5 which was predicted to cause a major structural defect in the collagen IV alpha5 chain. Despite angiotensin-converting enzyme inhibitor therapy his proteinuria progressed to the nephrotic range associated with edema. At the age of 7 years, cyclosporine therapy was instituted, which promptly resulted in almost complete resolution of proteinuria. Three years later his urinary protein excretion was close to the normal range and serum creatinine remained within normal limits. We conclude that closely monitored cyclosporine therapy may be a safe and effective treatment in patients with severe proteinuria and Alport syndrome.