BACKGROUND: To study the psychometric properties of a modified Alcohol Use Disorders Identification Test in the multilingual context of Switzerland. METHODS: Data were obtained from the most extensive health survey to date in Switzerland, with a response rate of 69%. Seven core items of AUDIT were used. The first two items of AUDIT (frequency of drinking, quantity of drinking) were not used in their original form, but reconstructed from a quantity-frequency instrument (QF) measuring alcohol consumption, and categorized according to the AUDIT. The third AUDIT item (frequency of binge drinking) was similarly not used in its original form, but 8+ drinks instead of 6+ drinks was used. All 10 items of the modified AUDIT were completed by 10321 subjects - 6677 in the German-speaking region and 3644 in the Latin-language (French, Italian) regions. The dimensionality of the modified AUDIT was modelled by confirmatory factor analysis. The contribution of each item to the total modified AUDIT score was investigated by the prevalence of positively screened subjects when items were deleted, and factor loadings of the unidimensional model. RESULTS: In Switzerland the modified AUDIT fitted neither a unidimensional nor the hypothesized tri-dimensional model. Consumption items, especially frequency of drinking, showed almost no correlation with items measuring alcohol-related problems, but the latent constructs 'harmful drinking' and 'alcohol dependence' were highly correlated, indicating a shared underlying factor. Frequency of drinking was the item that most influenced whether an individual screened positively or not. Except for the correlation of frequency and binge drinking, results were almost identical for both linguistic regions. CONCLUSIONS: The current form of the modified AUDIT may have to be changed for screening in Switzerland, as the study raised questions about the suitability of the frequency-of-drinking item as an indicator of a screening device for alcohol-related problems in this country.