BACKGROUND Asthma remains a serious global health challenge. Poor control of asthma symptoms is due in part to incorrect use of oral inhaler devices that deliver asthma medications, such as poor inhalation technique or use of a metered dose inhaler (MDI) after the recommended number of doses is expelled. OBJECTIVE To review published research on the potential for patients to overestimate or underestimate the amount of asthma rescue medication in MDIs without integrated dose-counting mechanisms. METHODS We searched PubMed and EMBASE using search terms "dose counter and asthma" and "dose counter and metered dose inhaler" for English language publications up to July, 2012, with a manual search of references from relevant articles. RESULTS Up to 40% of patients believe they are taking their asthma medication when they actually are activating an empty or nearly empty MDI. Device design makes it impossible for an MDI to cease delivering drug doses at an exact point, and the number of actuations in an MDI may be twice the nominal number of recommended medication doses. Once the recommended number of medication doses is expelled, remaining actuations deliver decreasing concentrations of active medication and increasing concentrations of propellants and excipients. This phenomenon, called "tail-off," is particularly problematic when medications are formulated as suspensions, as are rescue medications to control acute bronchospasm. Reliable inhalation of rescue medication could reduce asthma-related morbidity. CONCLUSION By helping to ensure that patients receive accurate metered doses of asthma rescue medication to relieve bronchoconstriction, dose counters may help to improve asthma management.