An autopsy case of caffeine intoxication related to the consumption of caffeinated products, such as energy drinks and caffeine contained drugs, was reported. Case report: A male in his early twenties was working a night shift job. After work one morning he came home and was not feeling well. He was vomiting a great deal and could not move, so his family had him lay down to rest. That afternoon they discovered his death. Although the decedent was examined by postmortem computed tomography, his cause of death could not be determined. A forensic autopsy was performed to investigate his cause of death. Autopsy findings: There were no obvious injuries on his whole body. Only slight brain edema and congestion of other organs were observed, but no significant lesions were found in his organs. A yellowish granular substance was observed in the stomach, duodenum, and small intestine. Alcohol concentration was 0.01mg/ml in the blood and urine. GC-MS and LC-MS/MS analyses did not detect any chemical substance except caffeine from his blood and urine. By LC-MS/MS analysis, the caffeine level (p g/mL) was 182, 71, and 10700 in the blood, urine, and gastric contents, respectively. Results and discussion: The fatal level of caffeine in blood has been reported as >100 u g/ mL. Thus, the cause of death was diagnosed as caffeine intoxication. It was revealed that he had consumed many energy drinks to stay awake and alert. Because he had a history of feeling ill and vomiting, it is suspected that he had an excessive intake of caffeine. Energy drinks, unlike most medicines, are able to be consumed repeatedly, and caffeine intoxication is a possible result. The reporting of this case will enlighten the danger of repetitious and chronic consumption of caffeinated products, such as energy drinks and caffeine contained drugs.