Lymphangioleiomyomatosis (LAM) is a rare disease, occurring in women, characterized by cystic degeneration of the lungs, abdominal tumors, and proliferation of abnormal smooth muscle cells. Lung function abnormalities consist of impairment of the diffusion capacity (DL(CO)) and airflow obstruction. The objective of this study was to correlate the functional impairment with histologic measures of disease severity to identify predictors of disease outcome. Lung function of 143 patients and lung biopsies of 74 of these patients were reviewed for evidence of airway disease and scoring of disease severity. A positive response to bronchodilators was associated with more severe airflow obstruction, a predominantly solid pattern of LAM lesions in the lung biopsy, and greater rate of decline in expiratory flow. Airway inflammation, present in 61% of the lung specimens, was not associated with reversible airway obstruction and did not correlate with the severity of airflow obstruction. DL(CO) correlated best with the LAM histologic score (LHS), a demonstrated predictor of outcome. We conclude that reversible airway obstruction is found in LAM patients with accelerated loss of lung function and a predominantly solid pattern of LAM lesions. Impairment of DL(CO) correlates with LHS, a predictor of survival and time to lung transplantation.