A three-year-old male castrated Chihuahua presented to an emergency hospital for acute vomiting and ataxia. Based on his history and clinical signs, he was diagnosed with presumptive methylxanthine toxicosis secondary to chocolate ingestion. With supportive care, including oral activated charcoal, antiemetics, and intravenous fluids, he made a full recovery. Early diagnosis and treatment led to a successful outcome. Treatment of methylxanthine toxicosis is well­ established, and involves stabilization, decontamination, supportive care, and monitoring.