Proliferative activity of cerebellar juvenile pilocytic astrocytomas (CJPA) and its significance for prognosis was retrospectively investigated. Forty-four consecutive children operated between 1981 and 1997 with a mean age of 8.3 years (3 months to 20 years) were reviewed. Clinical and radiological follow-up was available for 38 patients ranging from 0 to 18 yrs (mean 6.3 years). Proliferative activity was determined by MIB-1 immunohistochemistry on sections of resected tumor specimen. Total resection was achieved in 35 children (79.5%), subtotal in 9 (20.5%). Currently, 31 are tumor-free, 6 have stable remnants, one developed spinal seeding and one died. Radiology revealed a cystic mural node type tumor in 27 patients (61.4%), a solid lesion with a small cyst in 5 patients (11.4%), and a solid tumor in 12 patients (27.3%). Mean MIB-1 labeling index (LI) of all tumors was 4.4% (range 0.6-12%, SD = 2.7) and did not correlate with age, gender, localization, amount of resection, follow-up status, histological appearence or grade of neovascularization, but showed a significant correlation to radiological types: 6.9% in solid tumors versus 3.7% in the cystic mural node type (p = 0.0037). Five year progression-free survival (PFS) of all patients was 84.4%, differences between subgroups of MIB-1 <5% (27 patients, PFS = 87.4%) and MIB-1 >5% (13 patients, PFS = 76.3%) were not significant. CJPA showed a remarkable high MIB-1 LI, but no significant correlation to PFS in this series. Nevertheless, radiologically solid tumors demonstrated a significantly higher MIB-1 LI and thus may need further investigation for possible increased ability of regrowth.