Objectives: The purpose of this study was to examine the cause of an accidental death from acute poisoning resulting from exposure to a cleaner containing tetramethylammonium hydroxide (TMAH) and to consider measures to prevent future cases. Methods: The authors examined the details and the reason for the accidental death from acute poisoning based on the autopsy report. Results: The victim was a 39-year-old male researcher with 7 years of work experience employed by a surfactant production company. The accident occurred when he was conducting a field test of a newly developed cleaner, containing 8.75% TMAH solution. The researcher spilled the cleaner on his work clothes in the area of both the hands/arms and legs. He was unconscious when discovered. An autopsy found no damage or injury that could have resulted in death other than burns to 12% of his body, and the cause of death was found to be acute poisoning by TMAH. Discussion: TMAH is widely used in the electronics industry as a developer or cleaner. It is a dangerous material, causing neurotoxicity leading to respiratory failure by ganglion block that occurs through skin absorption, and no antidote has been developed yet. For this reason, it is best to completely prevent exposure by wearing proper personal protective equipment. Despite this fatal toxicity of TMAH, it is not classified in Korea as a “chemical requiring legal control”. For this reason, it is urgent to raise awareness of the toxic properties of TMAH to prevent additional cases of TMAH poisoning.(J Occup Health 2013; 55: 120–124)