Purpose: We report the first case in English literature of a posterior cerebral artery aneurysm encased within a lipoma. Methodology: Prospective review Results: A 80-year-old man presented with a longstanding head and hand tremor. A time-of-flight MR angiogram of the brain discovered a saccular left posterior cerebral artery aneurysm measuring 7x4mm in diameter within the interpeduncular fossa, partially encased within a T1 hyperintense lipoma 13mm in diameter. After multi-disciplinary discussion, the authors decided upon conservative management with surveillance. At 12 months, the patient remained asymptomatic and a repeat CT-angiogram was stable. Conclusion: Intracranial lipomas are associated with brain malformations (including cerebral artery abnormalities) in 55% of cases (1,2). They rarely justify surgical management; However, aneurysms of this size in the posterior cerebral artery have a significant 5-year rupture rate of 14.5%(3). In this case, the aneurysm being encased within the lipoma would increase the operative complexity if accessed by microsurgical means, and the lipoma wrapping the aneurysm itself may provide protection against subarachnoid haemorrhage. On balance, it was deemed reasonable to conservatively manage his aneurysm. References 1. Truwit CL, Barkovich AJ. Pathogenesis of intracranial lipoma: an MR study in 42 patients. AJR Am J Roentgenol. 1990 Oct;155(4):855–64; discussion 865. 2. Macpherson RI, Holgate RC, Gudeman SK. Midline central nervous lipomas in children. Can Assoc Radiol J J Assoc Can Radiol. 1987 Dec;38(4):264–70. 3. Yilmaz N, Unal O, Kiymaz N, Yilmaz C, Etlik O. Intracranial lipomas—a clinical study. Clin Neurol Neurosurg. 2006 Jun;108(4):363–8.