[en] Background: Patients with anorexia nervosa (AN) are at high risk of renal failure. Glomerular filtration rate (GFR) is overestimated when estimated by the creatinine-based equations. We have studied the accuracy and precision of cystatin C-based equations. Method: 27 AN patients were included. GFR was measured with the chromium-51-ethylenediaminetetraacetate (51Cr-EDTA) method. We have compared the accuracy and precision of creatinine-based equations (MDRD and Cockcroft) with those of different new cystatin C-based equations. Results: The creatinine-based equations overestimate measured GFR, especially the MDRD study equation. All the cystatin C-based equations also overestimate measured GFR. The Cockcroft and Gault formula and the cystatin C-based equation published by Rule have the best accuracy and precision, but these last performances remain unsatisfactory. Conclusion: Both creatinine and cystatin C-based equations strongly overestimate measured in patients with AN.