In the prospective consecutive Danish Aneurysm Study 192 patients (19%) had a ruptured intracranial aneurysm (RA) with a maximum diameter < 5 mm (small). In 524 (51%) and 306 patients (30%) the size was 5-10 mm (medium) and 11-24 mm (large), respectively. More patients with large RA (35%) were unconscious more than 1 h after the bleeding and had more CT-visualized haematomas (49%) compared with the patients with small RA (28 and 34%) and medium RA (27 and 37%). After 2 years, more patients with small RA and medium RA had resumed their previous occupation (49 and 49%), regained a normal daily functional capacity (55%, 55%) and normal mental outcome (29 and 32%) compared with the patients with large RA (34, 44 and 23%). The mortality was 47, 39 and 51% for patients with small, medium and large RA, respectively. With also a very serious prognosis after rupture of aneurysms of 10 mm or less and even less than 5 mm we also recommend surgical treatment of unruptured aneurysms of these sizes.