Purpose: Pilocytic astrocytoma( PA) is low grade glioma occurring in young age. Treatment with gross tumor resection(GTR), whenever possible, yields better long term outcome than other approaches. However, the optimal first-line treatment modality for subtotal resection (STR) group is remained to be elucidated. We aimed to determine efficacy of each first-line treatment modalities for STG group. Methods: We reviewed medical records of 104 patients retrospectively, who had been diagnosed as pilocytic astrocytoma at Yonsei University Health System from January 1983 to December 2012.. Kaplan-Meier analysis was performed to assess overall survival (OS) and progression free survival ( PFS). Cox proportional hazard models were used to calculate hazard ratios. Results: Total 38 patients received gross total resection, 52 patients had subtotal resections, and 5 patients had gamma-knife surgery (GKS). STR group underwent following first-line modalities; observation (N=34), treatment [total N=18, radiotherapy (N=11), chemotherapy (N=6) and GKS (N=1)]. In total group, 10-year OS was 91.5% and 10-year PFS was 56.2 %. In GTR group, 10 year OS was 96.7%, and 10 year PFS was 96.7%. In STR group, 10 year OS was 88.1% and 10 year PFS was 39.1%. 10year PFS in STR group was as follow: chemotherarpy group 66.7%; radiotherapy group 47.1%, observation group 28.0% ( P=0.040). In multivariate analysis for STR group, chemotherapy was superior to observation (Hazard ratio (HR)=0.031, P=0.008), Radiotherapy showed the tendency of survival benefit comparing with observation (HR=0.227. P=0.058). Conclusion: In STR group, postoperative treatment is better than observation. Postoperative chemotherapy and radiotherapy are all possible first-line treatment options for subtotally resected pilocytic astrocytoma patients.