<p>Nitrous oxide (N₂O) abuse is becoming increasingly popular worldwide. Moreover, the use of N₂O combined with other substances, such as alcohol, is also common. Accidental deaths associated with N₂O abuse are rare in forensic practice, with most fatal cases involving continuous inhalation equipment or exposure in a confined space. In contrast, the inhalation of N₂O using balloons is traditionally regarded as a relatively safe method. In this report, we present an unusual fatal case of a 16-year-old girl who died after drinking alcohol and inhaling N₂O from balloons. The decedent was found in a prone position with the nose and mouth compressed against the bed. Cyanosis of nails, pulmonary and cerebral edema, and the positive expression of HIF-1α in lung, myocardium and brain, were indicative of asphyxiation. Toxicological analysis revealed a peripheral blood ethanol concentration of 140&#xa0;mg/dL and cardiac blood N₂O concentration of 74.5 μL/mL. N₂O was also positively detected in the lungs, stomach contents, gastric air, and the brain. In conclusion, we determined that the decedent died from accidental asphyxia related to N₂O inhalation, prone positioning, and alcohol consumption. We also investigated chronic N₂O abuse from a forensic perspective. This report aims to help forensic pathologists manage similar cases. It also reminds N₂O abusers of potential dangers.</p>