Open lung biopsy in a 38-year-old female with Pringle-Bourneville syndrome and recurrent pneumothorax revealed a micronodular pneumocyte II hyperplasia, a new entity probably associated with the tuberous sclerosis syndrome. The lesion caused an obstruction of the alveolar lymphatic vessels and alveolar ducts, resulting in an emphysema-like picture. This cystic dilation of alveoli and draining lymphatics followed by rupture caused the recurrent pneumothorax. The epithelial pneumocytic nature of the lesion was confirmed by immunohistochemistry and electronmicroscopy.