Although many wild mushrooms are harmless, others are potentially toxic. This retrospective case series evaluated 3 dogs with known mushroom ingestion (either witnessed or found following vomiting or gastric lavage) that developed respiratory arrest after presenting to the hospital with vomiting, tremors, and/or ataxia. None of the patients reportedly had access to any other toxin. IV diazepam was administered in 2 dogs, although it was unclear whether it had any clinical efficacy; these dogs recovered uneventfully after intensive supportive care, including manual or mechanical ventilation, IV fluids, and injectable medications. The third dog’s owners elected humane euthanasia because of clinical deterioration. Mushroom analysis was performed in only 1 case; however, neurologic or respiratory effects were not associated with mushrooms identified in this case. It was theorized that a previously unidentified or unknown compound or a mushroom type not recovered in the vomitus caused the clinical signs. One mushroom species, Amanita spp, is known to contain muscimol, a biologically active GABA analog. GABA stimulation causes respiratory arrest/apnea, and it is thought that a GABAergic compound was the underlying cause of severe clinical signs in these 3 dogs.