Case Description: A 3 month old male puppy was evaluated for acute ataxia and obtunded mentation after suspected mushroom ingestion in June of 2009. A presumptive diagnosis of Amanita muscaria toxicosis was made following identification of the mushrooms brought in by the owner from his backyard. Clinical Findings: Physical examination and laboratory abnormalities included acute forebrain or multifocal encephalopathy, generalized muscle twitching, hypersalivation, hyperthermia, tachycardia, tachypnea, hyperproteinemia, hyperglycemia, pre-renal azotemia, metabolic alkalosis, hypernatremia, hypokalemia, and mild hypoxia. Treatment and Outcome: Administration of supportive and symptomatic therapies over 15 hours resulted in normalization of neurologic deficits and complete recovery. Clinical Relevance: Ingestion of A. muscaria mushrooms by dogs can result in acute and severe gastroenteritis or central nervous system dysfunction primarily from the toxic effects of ibotenic acid, muscimol, and muscarine. Even with severe clinical symptoms, the prognosis is excellent and full recovery is expected with appropriate supportive and symptomatic therapies.