BACKGROUND: With the advancement of cardiorespiratory interventions, the survival rate among patients with Duchenne muscular dystrophy (DMD) has increased. Subsequently, pneumothorax has become a significant problem in patients with prolonged ventilatory support. RESEARCH QUESTION: What are the frequency, recurrence rate, risk factors, and prognosis of pneumothorax in patients with DMD requiring noninvasive ventilation (NIV)? Also, are there known risk factors of pneumothorax on chest CT scans? STUDY DESIGN AND METHODS: This retrospective longitudinal cohort study included 176 patients treated between 2006 and 2019. We collected information regarding location, severity, treatment methods, recurrence frequency, abnormal findings on CT scanning, and date of death. We compared the pneumothorax and nonpneumothorax groups. We calculated the estimated survival probabilities from the age at NIV application according to pneumothorax occurrence. RESULTS: Sixteen of the 176 patients (9.0%) experienced pneumothorax (median age at diagnosis, 24.6 years; range, 20.7-33.7 years). Among the 16 patients, 15 demonstrated pneumothorax after NIV application (median time between diagnosis and initial NIV application, 5.6 years; range, 3 days-9.6 years). Sixteen patients experienced 31 episodes of pneumothoraces (range, one-five episodes); among them, seven episodes (22.6%) were asymptomatic. Known risk factors not clearly visible by radiography scans were found in chest CT scan in 11 patients (68.8%). Seven of 16 patients (43.8%) eventually sustained severe lung damage with pulmonary fibrosis. No significant between-group differences were found in body weight, BMI, and age at NIV application; however, the pneumothorax group showed a significantly higher mortality rate after NIV application. INTERPRETATION: On pneumothorax occurrence in patients with DMD, recurrences and severe lung damage are common; moreover, these patients show higher mortality rates than patients without pneumothorax. Chest CT scans should be performed to identify risk factors, and treatment should be initiated accordingly. In addition, physicians should consider chest CT scanning in the case of suspected pneumothorax, even if no radiographic abnormality is found.