Mushroom poisoning leading to acute renal failure is extremely rare in North America. Cortinarius species and Amanita smithiana both can cause acute renal failure and inhabit the Pacific northwest. This article describes 4 patients who presented in acute renal failure and who ingested mushrooms described as resembling A. smithiana. Two patients (a 74-year-old Korean couple) described eating mushrooms with an approximately 6 x 0.5-inch stipe with a white cap, 1.25-1.5 inches in diameter. The other 2 patients (a 55-year-old male and a 30-year-old female) also described a white-capped mushroom. All believed they were eating the matsutake (Tricholoma magnivalere) mushroom, which can be mistaken for A. smithiana. Onset of gastrointestinal symptoms ranged from 20 minutes to 12 hours, and presentation in acute renal failure ranged from 4 to 6 days postingestion (initial BUN and creatinine were 72-91 mg/dL and 12-13.9 mg/dL, respectively). One patient had underlying mild renal insufficiency and one had hypertension that was under control, while the others had no risk factors for renal disease. None had any other explanation for the episode of acute renal failure. All underwent acute hemodialysis for at least several weeks, eventually returning to baseline renal function.