BACKGROUND: Hydrogen peroxide is a common household product. It is clear and odorless making it easy to confuse with water, especially when improperly stored. Concentrated formulations are also available for consumer purchase. OBJECTIVE: We report a case of hydrogen peroxide ingestion in a child and discuss the potential consequences and treatment of such an exposure. CASE REPORT: A 12-year-old boy accidentally ingested a sip of concentrated hydrogen peroxide. He rapidly developed hematemesis and presented to the Emergency Department. His initial work-up was unremarkable, and his symptoms resolved quickly. However, diffuse gas emboli were found within the portal system on abdominal computed tomography. The child was treated with hyperbaric oxygen therapy and later found to have gastric irritation as well as an ulcer on endoscopy. He recovered fully from the incident. CONCLUSIONS: We present this case to increase awareness of the dangers of hydrogen peroxide ingestion in children. Fortunately, the child in this case recovered fully, but emergency physicians should be aware of the potential consequences and therapeutic options.