The aim of this review is to discuss the methodological issues involved in using pharmacy-record databases of drug sales in pharmacoepidemiology and to illustrate the usefulness of such data in estimating disease prevalence, patient adherence and persistence to therapy. Recent studies show that asthma/chronic obstructive pulmonary disease (COPD) prevalence increases with age. The volume of acquired asthma/COPD drugs per patient also increases with age and was approximately 2.5-times higher for patients aged 60-69 years compared with patients aged 20-29 years. Despite this, there is a comparatively low interest in asthma/COPD research involving elderly individuals. Published asthma/COPD-prevalence data and drug-treatment-prevalence data correspond reasonably well. Short- as well as long-term studies on drug acquisition indicate that approximately a third of patients have drugs available to cover at least 80% of the prescribed treatment time. Only approximately a tenth of the patients acquired steroids or steroid combinations, corresponding to one daily defined dose per day over a 5-year treatment period. It is probable that asthma/COPD is undertreated in all age groups.