This study from Danish general practice with the participation of 131 practices covering a population of 450,000 persons assesses all consultations concerning asthma during a 1-year period from June 1977. Asthma was defined as paroxysmal bouts of dyspnoea of an expiratory type. Results are presented from three groups of practices differing in their self-estimated rate of reporting. A total of seven to nine per 1000 of the population contacted a general practice during the study year (men: 7-10, women: 6-8). The prevalence may be described by a two-peaked curve with maxima at ages 5-14 years and 50-70 years. In the former group the prevalence rate among boys is double that of girls. In the later group asthma is more common among women until the age of 55, after that age it is more common among men. More than half of the patients consulted with symptoms during the study year. The isle of Fyn had a lower prevalence rate with and without symptoms that all other regions. The consultation rate was 5.7 per asthma patient per year. In about 25-30% of these consultations patients presented with symptoms. The isle of Fyn had the lowest consultation rate.