The burden of asthma is increasing in terms of prevalence, severity of symptoms and other markers of asthma control. Poor control of symptoms is a major issue that can result in adverse clinical and economic outcomes. Prescribing costs are the most obvious and visible expense in asthma care but these are but the tip of the iceberg. We need to take all factors into account when considering the overall costs of asthma treatments and recognise that treatment that results in better asthma control may result in lessening of both direct and indirect costs. To assess this accurately, health economic evaluations need to be undertaken in relevant settings, on representative populations. They need to use appropriate measures of asthma outcome. Drug-related costs need to take into account savings made by decreased costs of other prescribed medication and patient factors must be taken into account. We need information that is applicable to the types of patients we see in the real world to make proper cost analyses. Such information can come from 'pragmatic' randomised trials, from retrospective claims analysis from observational studies or using primary care clinical and prescribing databases.