We report on 50-year-old woman without tuberous sclerosis, presenting with recurrent spontaneous pneumothorax. A CT-scan of the chest showed multiple, bilateral, thin-walled cysts, consistent with pulmonary lymphangioleiomyomatosis. A videothoracoscopic lung biopsy confirmed the diagnosis of lymphangioleiomyomatosis, but revealed also a micrometastasis from an occult papillary carcinoma of the thyroid gland. The main histologic differential diagnosis and the possible correlation between lymphangioleiomyomatosis and thyroid diseases are briefly discussed.