Dissemination of glioblastomas is often observed, but the underlying mechanism is not well clarified especially from the genetic viewpoints. The present study examined whether PTEN gene mutations and MIB-1 labeling index (LI) correlate with the dissemination in 39 consecutive patients with glioblastomas. Dissemination was defined as leptomenigeal enhancement by magnetic resonance imaging performed in all patients every 2-3 months. We examined PTEN mutations in 26 patients using cDNA-based direct sequencing and MIB-1 LI in 38 patients. Median survival time of the 39 patients was 16.2 months. Dissemination was found in 17 of 39 patients (43.6%). PTEN mutation was significantly associated with dissemination (P=0.0140), and higher MIB-1 LI (> or =35%) resulted in earlier dissemination (P=0.0156). Kaplan-Meier survival plots showed a significantly poorer survival for patients with PTEN mutation (P=0.0012). The results indicate that the evaluation of PTEN mutation and MIB-1 LI are useful to predict dissemination and prognosis of glioblastomas.