Gliomatosis cerebri (GC) is a specific entity defined as diffuse infiltration of neoplastic glial cells into at least three cerebral lobes and preservation of the surrounding neuronal architecture. We report a patient with secondary GC that mimicked clinicoradiological features of limbic encephalitis (LE). A 72-year-old man had developed headache and disorientation insidiously 2 weeks previously. On admission, neurological examination showed confusion and hyperreflexia in the right extremities. Brain magnetic resonance imaging (MRI) revealed T2-hyperintensity in bilateral frontal, the left parietal, the left temporal lobes and bilateral posterior periventricular zones. Slight enhancement existed in the left lower temporal region. Cerebral angiography exhibited no tumor stains. Repeated cerebrospinal fluid studies showed mild pleocytosis and cytology of class I. There were no infectious pathogenic agents. His neurological symptoms were ameliorated at 7 days after treatment with dexamethasone and glycerol. Follow-up MRI showed no pathognomonic changes. Mild memory dysfunction remained. He was diagnosed as LE of unknown cause. Three months later he became disorientated. Brain CT revealed a hemorrhagic mass with surrounding edema in the left temporal, frontal and parietal lobes. MRI displayed marked enhancement in these regions. Urgent neurosurgery was performed and glioblastoma multiforme (GM) was confirmed pathologically. The early clinicoradiological course of this patient suggested similarities to LE. At 3 months after clinical onset, the neuroradiological features reflected rapid transformation from secondary GC to massive GM. Thus, it is important to pay more attention to the differential diagnoses of GC and LE in patients who have memory deficits and widespread MRI lesions.