BACKGROUND: Lymphangioleiomyomatosis (LAM) is a rare lung disease characterised by progressive airflow obstruction. No effective medical treatment is available but therapy with sirolimus has shown some promise. The aim of this observational study was to evaluate sirolimus inprogressive LAM. METHODS: Sirolimus (trough level 5 - 10 ng/ml) was administered to ten female patients (42.4 ± 11.9 years) with documented progression. Serialpulmonary function tests and six-minute-walk-distance (6-MWD) assessments were performed. RESULTS: The mean loss of FEV1 was -2.30 ± 0.52 ml/day before therapy and a significant mean gain of FEV1 of 1.19 ± 0.26 ml/day was detected during treatment (p = 0.001). Mean FEV1 and FVC at baseline were 1.12 ± 0.15 l (36.1 ± 4.5%pred.) and 2.47 ± 0.25 l (69.2 ± 6.5%pred.), respectively. At three and six months during follow-up a significant increase of FEV1 and FVC was demonstrated (3 months ΔFEV1: 220 ± 82 ml, p = 0.024; 6 months ΔFEV1: 345 ± 58 ml, p = 0.001); (3 months ΔFVC: 360 ± 141 ml, p = 0.031; 6 months ΔFVC: 488 ± 138 ml, p = 0.006). Sirolimuswas discontinued in 3 patients because of serious recurrent lower respiratory tract infection or sirolimus-induced pneumonitis. No deaths and no pneumothoraces occurred during therapy. CONCLUSIONS: Our data suggest that sirolimus might be considered as a therapeutic option in rapidly declining LAM patients. However, sirolimusadministration may be associated with severe respiratory adverse events requiring treatment cessation in some patients. Moreover, discontinuation ofsirolimus is mandatory prior to lung transplantation.