The current report describes a 13-month-old boy with primary pulmonary rhabdomyosarcoma (RMS) that originated within a congenital cystic adenomatoid malformation (CCAM). To the best of our knowledge, he is the youngest patient of all primary pulmonary RMS cases reported in the English-language literature. The tumor, localized in left upper lobe, was removed completely, and histologic examination showed embryonal subtype. Postoperative systemic chemotherapy was carried out. Recent evaluation 15 months after resection has not identified any residual or recurrent disease. Primary pulmonary RMS, although very rare in the pediatric age group, should be considered in young patients with solitary pulmonary masses and associated cystic lesions. Copyright 2001 by W.B. Saunders Company.