Background: Pulmonary Langerhans cell histiocytosis (PLCH) is a smoking-related interstitial lung disease characterized by development of cystic changes that predispose to occurrence of pneumothorax. Study objectives: To determine the frequency, recurrence rate, and optimal management of pneumothorax associated with PLCH. Design: Retrospective study. Setting: Tertiary care, referral medical center. Patients: One hundred two adults greater than or equal to 18 years old with histologically confirmed PLCH seen at Mayo Clinic Rochester over a 23-year period from 1976 to 1998. Interventions: None. Measurements and results: Sixteen of 102 patients (16%) with PLCH had pneumothorax; mean age at the time of diagnosis was 29.4 years (range, IS to 52 years), and all had smoked cigarettes. There were 37 episodes of pneumothoraces (I to 5 episodes per patient); 10 patients (63%) had more than one episode. Median age at diagnosis of PLCH was significantly younger in patients with pneumothorax when compared to those without pneumothorax (27 years vs 41.5 years, p < 0.001), but pulmonary function parameters and survival after diagnosis were not significantly different. Rate of recurrent pneumothorax was 58% to the ipsilateral side when the episode was managed by observation or chest tube without pleurodesis, and 0% after surgical management with pleurodesis. Conclusions: These data support the early use of surgical therapy with pleurodesis in managing patients with PLCH and spontaneous pneumothorax.