Correlations were made between clinical and follow-up data and histopathologic findings in 105 women (mean age ± standard deviation, 38.3 ± 9.0 years) with pulmonary lymphangioleiomyomatosis (LAM). The actuarial survival (to pulmonary transplantation or death) of the patients from the time of lung biopsy was 85.1% and 71.0% after 5 and 10 years respectively. The histologic severity of LAM, graded as a LAM histologic score (LHS), was determined on the basis of semiquantitative estimation of the percentage of tissue involvement by the two major features of LAM: the cystic lesions and the infiltration by abnormal smooth muscle cells (LAM cells) in each case: LHS-1, <25%; LHS-2, 25% to 50%; and LHS-3, >50%. Analysis using the Kaplan-Meier method revealed significant differences in survival for patients with LHS-1, -2, and -3 (p = 0.01). The 5-and 10-year survivals were 100% and 100% for LHS-1, 81.2% and 74.4% for LHS-2, and 62.8% and 52.4% for LHS-3. Increased degrees of accumulation of hemosiderin in macrophages also were associated with higher LHS scores (p = 0.029) and a worse prognosis (p = 0.0012). Thus, the current study suggests that the LHS may provide a basis for determining the prognosis of LAM.