Aim: The aim of this work was to assess the respiratory functions of ambulatory Duchenne patients and to propose an earlier time period for intervention. Materials and Methods: Lung functions and North Star Ambulatory Assessment (NSAA) scores of Duchenne patients were evaluated simultaneously. Results: Thirty ambulatory Duchenne patients were included in this study. NSAA scores of the patients were directly correlated with arm abduction, arm adduction, and shoulder flexion strengths. Forced expiratory volume in 1 second percent predicted and forced vital capacity (FVC) percent predicted correlated inversely to age and to the NSAA score. Twelve of 13 patients with FVC values lower than 80% of predicted had NSAA scores below 24 points. None of the patients who were younger than 7 years had FVC values lower than 80% of predicted. Conclusion: Annual spirometry is necessary for Duchenne patients older than 6 years regardless of the ambulatory status.