Conventional press-and-breathe metered dose inhalers (MDIs) are widely prescribed but are often difficult for many patients to properly use. A total of 501 patients from different medical specialties were enrolled in this study, which evaluated how the patients used their MDIs. Using a conservative method (minimum number of errors) of determining errors, we found that 388 (77.5%) of the patients made at least one error when demonstrating how they use their MDI for two observers. Using a liberal (maximum number of errors) method of analysis, we found that 447 (89.2%) of the patients made at least one error. There was no difference in errors made stratified by patient gender, patient age, or the medical specialty that treated the patient's pulmonary disease. The two most common errors made by patients were failure to breathe out to functional residual capacity before actuation (225 by minimum method, 280 by maximum method) and not actuating the canister at the start of inhalation (207 by minimum method, 323 by maximum method). Of the patients with improper timing of actuation, the majority (121 patients by minimum method and 187 patients by maximum method) actuated the canister early. In this large patient sample, regardless of which medical specialty provided the treatment, the majority of the patients evaluated had less than optimal MDI technique. Routine assessment of MDI technique should be instituted as standard practice care.