A 73-year-old male presented with a glioblastoma that was detected at the initial stage in the developmental process. He suffered cerebral infarction. Follow-up magnetic resonance (MR) imaging showed no abnormality. Ten months later, he had transient right hemiparesis. Diffusion-weighted and fluid-attenuated inversion recovery (FLAIR) MR imaging showed a hyperintense area in the left frontal lobe. The diagnosis was cerebral infarction and antiplatelet drug treatment was begun. The patient's right hemiparesis subsided. Ten days later, right hemiparesis reappeared. Diffusion-weighted and FLAIR MR imaging showed an enlarged hyperintense area in the left frontal lobe. Three weeks after the onset of right hemiparesis, MR imaging revealed an irregular ring-enhanced mass lesion that had further increased in size. The diagnosis was brain abscess and antibiotic treatment was initiated. However, the lesion did not respond and had further enlarged 5 weeks after the onset of right hemiparesis. The lesion was partially removed and the histological diagnosis was glioblastoma with Ki-67 labeling index of 26%. After surgical treatment, the patient received irradiation of 60 Gy and chemotherapy with temozolomide. Follow-up MR imaging showed regrowth of the tumor and aggravation of edema. The rapid progression of the tumor ultimately resulted in the patient's death 12 months after the onset of right hemiparesis. Diffusion-weighted imaging is a good method for the early detection of glioblastoma.