Estimation of time trends in alcohol consumption for recent years in Switzerland is complicated by the fact that the assessment method was changed from personal interview to self-administered questionnaire. With a large-scale study which compared the two methods, it is possible in estimating time trends to allow for adjustment of the effects produced by this change of assessment method. Results indicate that alcohol consumption decreased by about 17% between 1987 and 1993. This decrease was observed uniformly for both genders and all age-groups, which supports the basic assumptions of Skog's revised theory of Ledermann (1985). Personal interviews resulted in considerably higher reported alcohol consumption (+22%) than written questionnaires.