This study from Danish general practice gives figures about the simultaneous prevalence of asthma and allergic rhinitis and the order of onset among 7662 patients, who during 1 year consulted for one or both of these diseases. Twenty-eight percent of patients with asthma consulted because they also had allergic rhinitis, and 17% of patients with allergic rhinitis consulted because they also had asthma. Age- and sex-distributions are presented. In 25% of patients with both diseases the onset of both diseases occurred within the same year, while in 35% the onset of asthma occurred first and in 40% allergic rhinitis. Among patients with both diseases, who did not have onset of both within the same year, more than 75% of them had onset of one disease within 2 years of the other.