Objective To study clinicopathologic features, treatment and prognosis of pilocytic astrocytoma (PA). Methods Histopathological, ultrastructural, immunohistochemical(EnVision method) and clinical features of 68 cases of PA were studied by microscopic investigation with correlation of clinical follow-up information when available. Results Thirty-five male patients and 33 female patients were studied The patient's age ranged from 3 to 66 years (mean=20.1 years). The mean time from symptom onset to surgery was 371 days (range,3 days to 14 years). Cystic degeneration was noted in 41 cases (60.3%), and enhancement of the tumor was noted in 43 cases (87.8%). On postcontrast imaging examination there were 33 cases involving the cerebellum (48.5%). Total tumor excision was performed in 35 patients, subtotal tumor excision was performed in 31 patients, and the procedures of other 2 patients were not clear. Among 51 patients with follow-up information, 44 were alive, 7 had recurrent tumor, and 7 died The post-operative survival ranged from 2 months to 124 months (mean survival=48.1 months). Five years and ten years survival rates were 89%, respectively. Tumors with classic histopathology demonstrated biphasic pattern of growth, consisting of compact elongated bipolar astrocytes associated with rosenthal fibers, and less cellular areas of multipolar cells with granular bodies and microcyst. Some cases showed atypia of nuclei, and occasional mitoses. Involvement of subarachnoid space was seen in 17 cases. One case had anaplastic features. All cases showed diffuse positive staining for GFAP and low expression for Ki-67, except 1 anaplastic tumor with 10% Ki-67 indices. Tumors with snharachnoid space involvement showed positive reticular fiber staining and negative EMA staining. Conclusions PA is a benign, WHO grade I tumor with favorable prognosis, and does not require radiotherapy after total resection. The tumor can be mistaken as higher-grade astrocytoma when involving the subarachnoid space, and with cytological atypia, leading to unnecessary radiotherapy after surgery. Recurrence rate is increased when only partial resection is achieved.The outcome for pafients with brainstem tumor or anaplastic PA is poor.