The lungs of three patients dying of lymphangioleiomyomatosis (LAM), which in two of the patients was associated with tuberous sclerosis, were studied to characterize better the sites of airflow limitation in this condition. Quantitative studies showed that small airways were narrowed and collapsed because of the surrounding emphysema, but few airways contained excess smooth muscle. These findings suggest that the airspace lesions are more important than muscular proliferation in small airways in producing airflow limitation. In the two patients who had LAM with tuberous sclerosis, sex steroid assays were negative. Pleurodesis controlled pleural effusions in all three patients but may have contributed to reductions in lung volume.