Over the past 9 months, three cases of primary pulmonary rhabdomyosarcoma have been treated at British Columbia Children's Hospital. Two patients (aged 24 and 37 months) presented with spontaneous pneumothoraces and had cystic changes in the affected lung on chest radiograph. The third patient (aged 42 months) was evaluated for chronic cough, fever, and failure to thrive. Chest x-ray showed a large mass in the left lower lobe as well as mediastinal adenopathy. All three of these lesions originated within congenital lung cysts, one a peripheral bronchogenic cyst and the others cystic adenomatoid malformations. This report suggests that there is a significant risk for the development of rhabdomyosarcoma within malformed pulmonary tissue.