OBJECTIVE AND IMPORTANCE: Although the presence of a foreign body in the cranium after a head injury is a well-known entity, cases of retained intracranial foreign bodies causing a delayed onset of neurological symptoms are rare. To our knowledge, an unrecognized intracerebral glass particle mimicking a cavernoma has not been previously reported in the literature. CLINICAL PRESENTATION: We report a unique case regarding an intracranial foreign body. A 39-year-old patient presented with new-onset epilepsy. The patient had no history of trauma. According to the magnetic resonance imaging findings and the patient's clinical course, the responsible lesion was considered to be a temporal cavernoma. INTERVENTION: During the operation, surprisingly, a glass particle was found within the temporal lobe. The glass had penetrated the cranium during a minor head injury and had remained undetected for 33 years. The patient was seizure-free without medication during 3 years of follow-up. CONCLUSION: Intracranial small foreign bodies can be difficult to diagnose, especially in patients with no history or a vague history of head trauma. Patients with long-standing retained foreign bodies may remain clinically well until complications arise. Intracranial foreign bodies may mimic other pathologies clinically and radiologically. Copyright © Congress of Neurogical Surgeons.