Background: The quality of the inhalatory technique (IT) is a factor on which its therapeutic success relies. Objective: Evaluate the quality of the IT performed by mothers of hospitalized infants due to acute respiratory infections, identifying possible mistakes. Method: 10 steps of an optimal IT were evaluated through a numerical scale previously designed, each step qualified with score 0 or 1 according to its accomplishment (maximum 10 points). The IT of each mother was evaluated and the correct accomplishment percentage of each step was calculated. Results: Mothers' IT scores presented a range of 4 to 10 points, where 12.5% reached the maximum score. The steps with the least accomplishment percentages were: appropriate waiting time between 2 inhalations (17.2%), performance of a second inhalation (83.6%) and holding the mouth and nose inside the inhalatory chamber for 10 seconds or 10 respiratory cycles once the inhalation had been administrated (89.1%). Conclusion: Although the majority of mothers had received IT instruction and are familiarized with it, certain steps are still performed in a deficient way, compromising the therapy success