The authors present the case-records of three patients who became intoxicated with the mushroom Cortinarius orellanus. This mushroom is very rare in this country and is not well known. The toxin orellanin is solely nephrotoxic and renal affection can lead to acute renal failure. A specific feature of this intoxication is the symptom-free period from 2 to 21 days, gastrointestinal complaints associated with back pain. The diagnosis can be established from a mycological analysis or by estimation of toxin in serum or tissue obtained by renal biopsy. The basis of treatment is disposal of the toxin by extracorporeal elimination methods: haemodialysis and haemoperfusion. As with the length of the interval between intoxication and onset of treatment the probability of irreversible renal affection increases, the medical community should take into consideration possible intoxication with this mushroom in the differential diagnosis of acute renal failure.