BACKGROUND: Although pilocytic astrocytomas (PA) generally are considered benign, a subset of patients with PA have disease progression despite standard treatment with surgery and radiation therapy. The authors report their experience with chemotherapy in this patient group. METHODS: The authors treated 11 patients (4 males and 7 females; median age at diagnosis, 8 years) with pathologically confirmed PA with chemotherapy. In eight patients, tumor progression or recurrence despite prior surgery and radiation therapy led to chemotherapy treatment. In three children younger than 5 years, chemotherapy was given in lieu of radiation therapy immediately after diagnosis (in one patient) or at the time of disease progression after surgery (in two patients). The authors used ten different chemotherapy regimens to treat the 11 patients. RESULTS: Chemotherapy produced clinical and radiographic improvement (R/R) in four (36%) patients, clinical stabilization and radiographic improvement (SD/R) in 1 (9%), clinical and radiographic stabilization (SD/SD) in 3 (27%), and was associated with clinical and radiographic progression (PD/PD) in 3 (27%). Three of the five patients with radiographic improvement had a greater than 75% reduction of maximal cross-sectional tumor area. Hematologic toxicity resulted in dose reductions in 43 of 110 (39%) total courses of chemotherapy. There were three hospitals admissions for fever and neutropenia and one chemotherapy-related death. CONCLUSIONS: The authors conclude that chemotherapy may benefit those with progressive inoperable PA. Chemotherapy may delay the need for radiation therapy in young patients with unresectable PA requiring treatment. PA may be a chemosensitive primary brain tumor.