We evaluated the efficacy of cyclosporin A (CyA) for treating pediatric patients with severe Henoch-Schönlein glomerulonephritis (HSP-GN) and nephrotic-range proteinuria. Seven pediatric HSP-GN patients (5 boys, 2 girls) were treated with CyA, with a mean age of 10.6 years at diagnosis (range 7.2-15.2 years) and mean follow-up times of 6.0 years (range 4.4-8.9 years) from diagnosis and 5.2 years (range 3.4-7.7 years) from the beginning of the CyA treatment. All had developed nephrotic-range proteinuria within 1-3 months of the HSP diagnosis. A renal biopsy was performed on all the patients, and two showed rapidly progressive glomerulonephritis. They all received additional angiotensin converting enzyme inhibitor medication and one to three types of immunosuppressive treatment had been tried in five of the seven patients before CyA was initiated at a mean interval of 0.7 years after diagnosis (range 0.1-2.0 years). All the patients responded to the CyA treatment within a mean of 1.4 months (range 1 week to 4 months). Four patients achieved a stable remission and had been without CyA treatment for a mean of 3.7 years (range 2.9-5.3 years) by the end of the follow-up. Three patients seemed to become CyA dependent, since they developed proteinuria when the treatment was stopped. CyA treatment had been started significantly earlier ( P=0.045) in the former group (mean 0.2 years, range 0.1-0.3 years) than in the latter (mean 1.5 years, range 1.2-2.0 years). Renal function was preserved in all patients, the glomerular filtration rate, plasma cystatin C, serum albumin, and serum creatinine being within normal limits at the end of the follow-up. We conclude that CyA treatment for severe treatment-resistant HSP-GN is promising, since four of the seven patients enjoy stable remission and all have retained their renal function after a mean follow-up of 6.0 years. However, some patients seem to develop CyA-dependent nephritis.