BACKGROUND: Wernicke encephalopathy is an acute neurological emergency caused by thiamine (vitamin B1) deficiency. The syndrome is associated with a significant morbidity and mortality, and prompt recognition and treatment of the syndrome in the emergency department (ED) is essential to improving patient outcomes. Numerous factors and clinical settings have been identified that predispose a patient to thiamine deficiency and subsequent Wernicke encephalopathy. CASE REPORT: We present the rare case of a 42-year-old man with a recent diagnosis of non-Hodgkin lymphoma who opted against chemotherapy in favor of a 60-day therapeutic water-only fast. On day 53 of his fast, the patient arrived to our ED in a coma and respiratory failure. Moments after the administration of thiamine, the patient's mental status and respiratory status improved significantly. Prior to admission and transport to the medical intensive care unit, the patient was awake, alert, and following basic commands. He was ultimately diagnosed with Wernicke encephalopathy. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: With the increasing incidence of patients choosing alternative medical therapies to treat a variety of diseases, numerous electrolyte, metabolic, and nutritional disorders are becoming increasingly more common in the ED setting. In some cases, patients may choose a therapeutic fast in an effort to combat a malignancy; the danger being that patients with cancers such as lymphoma are already at risk for thiamine deficiency as a result of the increased thiamine consumption associated with rapid cellular turnover. Wernicke encephalopathy is a life-threatening neurological emergency, and the emergency physician must be aware of the numerous predisposing factors to the condition, as early identification and treatment improves patient outcomes.