Smoking prevalence rates in Switzerland in the 1990s++ have been estimated from Perma data, which have been available quarterly since 1991, as well as from the data of the first and second Swiss Health Surveys, conducted in 1992/93 and 1997. Both sources--each providing data on more than 10,000 respondents--have been large-scale surveys that have used different but complementary survey designs. The probabilistic sampling design of the Health Surveys assures representative findings; the Perma data, although obtained through a non-probabilistic sampling design, permits trend analysis as Perma uses multiple measurement points and therefore time-series methodology can be applied. Both Perma and the Health Surveys yielded approximately the same prevalence of 37% male smokers in 1992/93 and 39% in 1997. For females Perma gave 4% higher prevalence rates than the Health Surveys (Surveys 1992/93: 24%; 1997: 31%). For both sexes the increase in total smoking prevalence was accounted for mainly by adolescents and young adults. Whereas the Surveys showed an increase from 29% to 41% (18% to 39%) in males (females) aged 15 to 19 years, the corresponding increase derived from Perma was 50% less. Except for this youngest age-group, differences between the methods remained within standard statistical norms. There is no doubt, however, that smoking in adolescents increased between 1992/93 and 1997.