Introduction 1 2 3 8 9 10 11 5 12 6 7 13 14 15 12 5 6 7 12 16 No study evaluated an additional control group without nephrotoxic therapy to demonstrate the physiological development of GFR in patients with SDNS. In this study, we focus on the long-term renal function in 20 children with biopsy-proven MCNS treated with CsA for a mean of 5.36 ± 2.2 (range 2–11) years. The development of GFR in these patients is compared with a control group with SDNS without CsA therapy. Patients and methods 17 18 2 19 2 18 20 2 2 Statistical analysis t p Results 2 2 2 1 1 p p 2 2 2 2 Table 1 2   n n Age at start of MCNS (years) 4.4 ± 2.2   4.0 ± 2.9  Age at start of CP (years) 5.7 ± 2.2 6.0 ± 3.2 Age at start of CsA (years) 8.4 ± 3.0 – CsA trough level at  month 12 (ng/ml) 98.8 ± 26.9 – Follow-up time (years) 5.4 ± 2.2 4.9 ± 3.4 GFR at start of CP 138.7 ± 24.6 p 137.7 ± 27.6 p Median 132 Median 131.6 Range 119–181 Range 95–196 GFR at stop of CP 130 ± 30.9 130.3 ± 24.7 Median 135.9 Median 131.1 Range 82–164 Range 93–178 GFR at start of CsA 136.3 ± 19.0 p  Median 136.5  Range 97–186  GFR at latest follow-up 114.5 ± 14.5 126.4 ± 19.8 p Median 114.2 Median 124.6 Range 89–135 Range 92–156 MCNS GFR Fig. 1 n  Fig. 2 n  2 2 2 2 p 2 p 3 4 Fig. 3 n  Fig. 4 n  1 Discussion 9 4 8 14 21 5 12 22 11 23 11 23 7 24 8 12 23 4 7 13 16 21 22 5 8 11 14 23 8 23 2 23 2 5 12 2 2 Interestingly, in our control group of patients without CsA therapy, an initial drop in GFR was also found. Those patients showed a mean drop in GFR of about 5% within the 12 weeks of CP therapy, and GFR even dropped about 8% until the latest follow-up. Probably, the observed decrease in GFR in patients with CsA therapy cannot only be attributed to the hitherto described nephrotoxic effect of CsA. 12 15 In summary, this study offers long-term follow-up of 20 patients with proven SSNS treated with CsA for a median of 5 years. Initially, the patients showed a drop in GFR but remained stable afterwards. None developed chronic renal failure. Nevertheless, the generalisation of these results are limited, as the study was retrospective, and only 5/20 patients underwent renal biopsy under long-term nephrotoxic treatment. It is questionable whether a prospective study to evaluate the outcome of long-term CsA therapy in children with MCNS is reasonable in the future. Newer, nonnephrotoxic drugs, e.g. mycophenolate mofetil (MMF) are of concern and need to be evaluated for efficacy and safety in the treatment of SDNS and FRNS. However, our analysis demonstrates that even long-term therapy with CsA for more than 5 years in children with MCNS is safe and does not impair renal function.