Aims: To assess the effect of mandatory thiamine enrichment of wheat flour on blood thiamine levels in an alcohol-dependent population. Methods: Alcohol-dependent clients (n = 100) entering an inpatient service for the management of alcohol withdrawal had thiamine blood tests and diet interviews. Approximately half (n = 46) the alcohol-dependent participants reported taking vitamin supplements prior to admission. Standard treatment included thiamine supplementation in the form of an intramuscular injection and 100 mg tablets. If consent was gained, a second thiamine blood test was taken prior to discharge (n = 77). Control participants (n = 20) with no history of treatment for alcohol abuse had thiamine blood tests and diet interviews. Results: Control participants consumed significantly larger amounts of thiamine in their diet compared with alcohol-dependent participants (P < 0.0001). Alcohol-dependent participants who reported no use of vitamin supplements had significantly lower (P < 0.05) blood thiamine levels compared with controls, whereas controls and those who reported using vitamin supplements had no significant difference. No significant correlation was found between thiamine blood levels and reported levels of alcohol consumption. Conclusion: Reduced blood levels of thiamine in people who are alcohol dependent, compared with those with no history of alcohol abuse, are likely to be because of the poor diet. Consumption of vitamin supplements appears to bring thiamine levels closer to those seen in control participants. Supplementation of dietary intake of thiamine in people who are alcohol dependent remains an important measure for the prevention of Wernicke–Korsakoff's syndrome in this population.