Background: Sirolimus, a mammalian target of rapamycin (mTOR) inhibitor, has been successfully employed for the treatment of carious type of vascular anomalies recently. Objectives: To evaluate the efficacy and safety of using oral sirolimus on vascular anomalies in single-center of a Korean university-setting hospital with cooperation of pediatric oncologist. Methods: Total 22 patients have used oral sirolimus longer than 3 months at vascular anomalies clinic of KNUH (avg.: 6.6±2.6 months). We evaluated therapeutic effects for 3 categories; clinical presentation (size/color/consistency), radiologic evaluation (USG/MRI), and health-related quality of life (pain/function/others). And we paid attention to development of side effect after using sirolimus. Results: Patients included LM/LVM (11 pts, 3 pts with KTS), VM (5 pts), tufted angioma (TA) (4 pts), and AVM (2 pts). Five patients (22.7%) including 3 TA and 2 LM showed improvement in all categories. Seven patients (31.8%) including 5 LM and 2 VM revealed improvement in 2 categories, but 3 patients (13.6%) including 1 LM, 1 AVM and 1 VM did no improvement in all categories. Oral ulcer was developed in 10 cases and diarrhea was occurred in 6 cases. And 2 patients were taken off medication due to severely recurrent oral ulcer. Conclusion: We cautiously suggest sirolimus may be an effective and well-tolerated therapeutic modality in selected patients with complicated vascular anomalies.