PURPOSE: To evaluate the role of radiotherapy in the management of incompletely resected supratentorial low grade astrocytoma with the analysis of the survival, the pattern of failure, and the prognostic variables affecting survival. MATERIAL AND METHODS: Between January 1990 and December 1995, fifty- one patients with supratentorial low grade astrocytoma received radiotherapy after subtotal resection(16 patients) or stereotactic biopsy(35 patients) at Asan Medical Center. External radiotherapy was done by conventional fractionation with the total dose of 4820cGy to 6000cGy(median 5580cGy) and partial brain volume. The follow-up was done from 6 to 79 months(median 48 months). RESULTS: Overall actuarial survival rate at 2 and 5 years were 83.4% and 54.8%, respectively. Progression free survival at 2 and 5 years were 67.4% and 48.7%, respectively. The significant prognostic factors affecting overall survival rate were the performance status, T stage, histologic subtype, radiation field and radiation response. The major pattern of failure was local failure, such as progressive disease and primary site recurrence in 23 patients (45.1%). Progression free survivors excluding 2 patients were physically and intellectually intact without major neurologic deficit. CONCLUSION: Although the follow-up period of this study was relatively short, overall actuarial and progression free survival rate were encouraging. Patients with good performance status, lower T stage, pilocytic subtype, patients treated with small radiation field and radiation responder showed better survival. As the local failure was the major pattern of failure, the various efforts to decrease the local failure is necessary.