BACKGROUND: Poor inhaler technique has been linked to poor asthma outcomes. Training can reduce the number of inhaler errors, but it is unknown which errors have the greatest impact on asthma outcomes. OBJECTIVE: The CRITical Inhaler mistaKes and Asthma controL study investigated the association between specific inhaler errors and asthma outcomes. METHODS: This analysis used data from the iHARP asthma review service-a multicenter cross-sectional study of adults with asthma. The review took place between 2011 and 2014 and captured data from more than 5000 patients on demographic characteristics, asthma symptoms, and inhaler errors observed by purposefully trained health care professionals. People with asthma receiving a fixed-dose combination treatment with inhaled corticosteroids and long-acting beta agonist were categorized by the controller inhaler device they used-dry-powder inhalers or metered-dose inhalers: inhaler errors were analyzed within device cohorts. Error frequency, asthma symptom control, and exacerbation rate were analyzed to identify critical errors. RESULTS: This report contains data from 3660 patients. Insufficient inspiratory effort was common (made by 32%-38% of dry-powder inhaler users) and was associated with uncontrolled asthma (adjusted odds ratios [95% CI], 1.30 [1.08-1.57] and 1.56 [1.17-2.07] in those using Turbohaler and Diskus devices, respectively) and increased exacerbation rate. In metered-dose inhaler users, actuation before inhalation (24.9% of patients) was associated with uncontrolled asthma (1.55 [1.11-2.16]). Several more generic and device-specific errors were also identified as critical. CONCLUSIONS: Specific inhaler errors have been identified as critical errors, evidenced by frequency and association with asthma outcomes. Asthma management should target inhaler training to reduce key critical errors. (C) 2017 American Academy of Allergy, Asthma & Immunology