PURPOSE: Glioblastoma (GBM) that presents as leptomeningeal disease (LMD) is extremely rare and fatal. Limited data are available regarding incidence, clinical presentation, and management. Prognosis is poor and no treatment is known to improve survival. METHODS AND RESULTS: We present a case report of a 72-year-old female who presented with depressed sensorium, ataxia, and myelopathy. Magnetic resonance imaging (MRI) showed diffuse supratentorial and spinal LMD. There was an absence of any detectable and distinct intraparenchymal lesion on neuroaxis imaging. Biopsy of the Sylvian fissure nodule revealed GBM. Steroid therapy was ineffective for symptom relief. She opted for palliative care and expired shortly after diagnosis. CONCLUSION: To our knowledge, this is the first reported case of GBM presenting exclusively as LMD without a primary lesion. If systemic imaging techniques do not provide a biopsy target and cerebrospinal fluid (CSF) studies are non-diagnostic, tissue diagnosis from leptomeningeal biopsy is recommended. Palliative chemoradiation or best supportive care are reasonable treatment options.