A 29-year-old woman presented with a sudden onset of a headache and 3 generalized tonic-clonic seizures. She was 30 weeks' pregnant, used cocaine, and had poor dental hygiene. Computed tomographic scans of her head showed diffuse subarachnoid hemorrhage and a hematoma in the left distal temporal region (Figure, A and B). Magnetic resonance imaging scans of her brain showed subarachnoid hemorrhage and a focus of signal void in the left distal temporal region (Figure, C and D). Magnetic resonance angiographic scans of her brain failed to detect an aneurysm (Figure, E and F). Computed tomographic scans (Figure, G-J) and catheter digital subtraction angiographic scans showed an aneurysm (size, 1.6 × 1.7 cm) in a distal branch of the left middle cerebral artery (Figure, K and L). The coil was unable to be placed owing to the distal location of the aneurysm. A cerebrospinal fluid sample and a blood culture showed no microbial growth, and a transthoracic echocardiogram showed no evidence of endocarditis. Serial computed tomography angiographic scans and serial digital subtraction angiographic scans showed complete thrombosis of the aneurysm in about 1 month. At 32 weeks and 3 days' gestation, she delivered by cesarean section. The patient was treated with levetiracetam, vancomycin hydrochloride, aztreonam, clindamycin hydrochloride, and nimodipine. Both the mother and neonate did well.