OBJECTIVE: To examine comorbidity and the medication load among asthmatics. Design A self-administered postal inquiry. SETTING: A national register-based random sample of 6000 subjects aged 16 years or older entitled to special reimbursement for anti-asthmatic medication in Finland. SUBJECTS: A total of 4690 subjects with clinically diagnosed asthma. MAIN OUTCOME MEASURES: Reporting of doctor-diagnosed chronic diseases and the number of prescription medicines used by asthmatics. RESULTS: Two-thirds of the subjects (n = 2952, 63%) reported other diseases in addition to other chronic pulmonary diseases and allergies. Musculoskeletal and cardiovascular disorders were the most common, increasing with age. Allergies were most frequent among the young asthmatics. Nearly all the subjects (n = 4444, 95%) took at least one anti-asthmatic medicine, and two out of every three (n = 3051, 65%) received other prescription medicines, most commonly cardiovascular drugs or analgesics. Some 41% (n=1938) of all the asthmatics and as many as 21% of the young adults (n = 269) were taking at least five prescription medicines concomitantly. The total medication load increased with age. CONCLUSION: The load of comorbidity and prescribed medication is heavy in adult asthmatics of all ages. Thus asthmatic patients should best be treated by GPs, while pulmonary specialists work as consultants and take care of the most severe cases.