The rupture of an aneurysm into an arachnoid cyst and subdural space is unusual. A 25-year-old man was admitted 2 weeks after having undergone a burr hole drainage for a chronic subdural haematoma elsewhere. An angiogram revealed a small aneurysm at the bifurcation of the middle cerebral artery. The aneurysm was clipped and the cyst communicated with the basal cisterns. To the best of our knowledge, this is the first report of an association of an aneurysm of the middle cerebral artery with an arachnoid cyst presenting as a chronic subdural haematoma.