Introduction: The use of inhaled medications remained as the pillar in pharmacological management of asthma and chronic obstructive pulmonary disease. Incorrect inhalation technique can impact drug delivery to the lung, compromised bronchodilation and lead to deteriorated disease control and worse disease outcomes. However, devices for inhaled medications can be difficult to learn and prone to mishandling despite presence of newer and more user-friendly inhalers. Objectives: This study aimed to assess and compare between patients’ self-rated confidence with their actual technique in using inhalers This study also aimed to determine factors associated with incorrect inhalation technique and impact of inhaler critical errors on clinical outcomes. Methodology: This was a cross-sectional study among patients with chronic respiratory disease who were users of inhalers, who visited outpatient pharmacy department and respiratory clinic, Serdang Hospital from 15th July to 15th August 2019. The patients were screened using convenient sampling according to inclusion and exclusion criteria. Pertinent data and inhalation techniques were identified during interview sessions. Results and discussion: Nearly a third of the patients who were confident with their inhalation technique had incorrect inhalation techniques and performed critical errors.