A 42-year-old woman presented with a 6-month history of diffuse headache of moderate intensity and gradual onset of generalized weakness, imbalance, apathy, memory decline, hypophonia, dysphagia, constipation and urinary incontinence. Clinical examination revealed several elements of a frontal lobe dysfunction including apathy with motor impersistence, presence of primitive reflexes, generalized hyperreflexia with bilateral Hoffman sign and ankle clonus. The biological workup was unremarkable and a brain computed tomography scan identified a giant olfactory groove meningioma. A prompt neurosurgical intervention helped to reverse the symptoms. This case illustrates the benefits of actively looking for treatable conditions in young patients presenting with acute or subacute dementia and emphasizes the pivotal role of early brain imaging.