The number of persons hospitalized for asthma and mortality from asthma have both shown an increasing tendency in many countries over the last few years. In Norway, 1.4% of the respondents in the 1975 Health Survey conducted by the Central Bureau of Statistics claimed to suffer from asthma. The corresponding number in 1985 was 2.4%. The prevalence of asthma was higher among subjects in rural than in urban communities. There are many sources of error linked to the studies discussed in this paper. Nevertheless, there are certain indications of a real increase in the prevalence of asthma, and analytical studies into the possible causes of this disease should be conducted.