beta-D-ethylglucuronide (EtG) is a stable Phase II metabolite of ethanol which can be detected in urine samples several days after elimination of ethanol. It is a useful diagnostic parameter for monitoring abstinence of alcoholics in alcohol withdrawal treatment. For this purpose, determination in urine is mainly performed by LC-MS, LC-MS/MS, or by GC-MS. For the mass spectrometric identification and detection of controlled substances in more sensitive fields such as forensic toxicology, workplace drug testing, doping analysis, and veterinary organic residue control, official guidelines have been released requiring a chromatographic separation and a minimum of two mass spectrometric transitions of the analyte. However, for detection of EtG none of the published LC-MS/MS methods could fulfill the minimum requirements of any of these guidelines. Therefore, an existing LC-MS/MS method has been modified by monitoring further MS/MS transitions instead of only one (deprotonated molecule [M - H](-)/product ions: m/z 75, 85, 113, and 159 optional) with the aim of withstanding administrative or court scrutiny in forensic or workplace drug testing cases. Full method validation has been performed in accordance to guidelines of the German Society of Toxicology and Forensic Chemistry (GTFCh) and requirements of ISO 17025. One application field in the United States is a workplace monitoring program to detect surreptitious alcohol use among recovering health professionals, who by contract had agreed on total abstinence after drug and alcohol withdrawal therapy.