Twenty-six young men with no previous medical history all ingested mushroom soup, exclusively made with Cortinarius orellanus. They were hospitalized 10-12 days after the incident. On admission, 12 patients presented with acute tubulointerstitial nephritis with acute renal failure; 8 required haemodialysis. In addition to symptomatic treatment, 9 patients were given corticosteroids. In this group of 12 patients, 8 recovered rapidly, and the other 4 suffered from chronic renal failure for several months. In the other group of 14 patients, initial leukocyturia was observed in 12 cases, although renal function remained normal during a one-year follow-up. Hepatic acetylation and hydroxylation tests performed after 6 months in 22 patients did not provide any explanation for the strong individual sensitivity to the renal toxicity of this fungus.