Two cases of lymphangioleiomyomatosis (LLM) of the lungs are compared, one with tuberous sclerosis and the other representing an isolated lung involvement. An increased frequency of complex chromosomal rearrangements was found in peripheral lymphocytes of the patient with tuberous sclerosis, in comparison to the patient with isolated lymphangioleiomyomatosis. Telomeric associations were found in cultured pulmonary smooth muscle cells from the patient with isolated LLM.