In Western countries alcohol misuse is the most frequent cause of thiamine (vitamin B1) deficiency (TD) and consequent neuro-impairment. Studies have demonstrated that between 30 and 80% of alcoholics are thiamine deficient, and this puts them at risk of developing the Wernicke-Korsakoff (WK) syndrome. The relative roles of alcohol and TD in causing brain damage remain controversial and it is important to try to determine the role played by each factor. Animal studies support an additive effect of alcohol exposure and TD, and indicate the potential for interaction between alcohol and TD in human alcohol-related brain damage. Early diagnosis of alcohol-related TD is therefore an important aspect of effective intervention and treatment. Alcohol biomarkers provide a direct and indirect way of estimating the amount of alcohol being consumed, the duration of ingestion and the harmful effects that long-term alcohol use has on body functions. Appropriate use of these markers is very helpful when considering a diagnosis of alcohol-related TD.