Rationale: Sirolimus has been shown in a randomized, controlled clinical trial to stabilize lung function in patients with lymphangioleiomyomatosis (LAM) treated for a 12-month time period; however the pretreatment decline in lung function after the drug was discontinued indicated that continued exposure is required to suppress disease progression. Objectives: To elucidate the durability and tolerability of long-term sirolimus treatment in Asian patients with LAM. Methods: We conducted a single-arm, open-label, investigator-initiated safety and efficacy study of sirolimus in 63 women with LAM at 9 sites in Japan. Subjects received sirolimus for 2 years at doses adjusted to maintain a trough blood level of 5-15 ng/ml. Measurements and Main Results: Fifty-two subjects (82.5%) completed the trial with mean drug compliance of more than 80% overall during the study. The number of adverse events was greatest during the initial 6 months of therapy, but they continued to occur with declining frequency throughout the 2-year study period. Of the 1,549 adverse events, 27 were classified as serious, including reversible sirolimus pneumonitis in 3 patients. New hypercholesterolemia occurred in