Subependymal giant cell astrocytoma (SEGA) is typically seen in children with tuberous sclerosis (TS), who present with headaches and seizures, and characteristic clinical and cutaneous manifestations of TS. Surgical resection, CSF diversion (for hydrocephalus), radiotherapy, and chemotherapy with a mammalian target of rapamycin (mTOR) inhibitor are treatment options. SEGA can occur in adults without TS, raising diagnostic and therapeutic challenges. A 53 year old man presented with headaches and diplopia. An exophytic, enhancing mass in the left lateral ventricle was resected, confirming SEGA. There was no recurrence on MRI 13 months later. He previously had an “astrocytoma” involving the left frontal horn resected at age 19. Pathology review was SEGA. He had no clinical or cutaneous findings of TS, and no family history of TS. An identical twin was well. A 66 year old man presented with “weakness”, due to diuretic-induced hypokalemia. CT showed a hypodense mass from the right caudate head deforming the frontal horn. MRI showed an exophytic, enhancing mass from the caudate head into the frontal horn. A stereotactic biopsy confirmed SEGA. He had no clinical or cutaneous findings of TS, and negative family history. His mother had a meningioma resected at age 66. Observation is planned. These 2 adult patients had SEGA without clear clinical findings or family history of TS. SEGA should be in the differential diagnosis of tumors involving the lateral ventricle.