Background A major challenge in the management of patients with unruptured intracranial aneurysms (UIAs) is the identification of criteria indicating a higher risk of future UIA rupture. Here we report a rare patient with documented short-term bleb growth of an UIA followed by fatal aneurysm rupture supporting the high-risk of rupture of short-term shape changes in UIAs. Case description A 72 year old man with an incidental unruptured anterior communicating artery aneurysm of 9 mm showed a bleb growth on the aneurysm sac at a 6 week follow-up CTA. Aneurysm treatment was recommended by the interdisciplinary board (PHASES score: 9 points, rupture risk 4.3%/5years). The patient wanted to discuss treatment plan with his family before final decision for treatment. Two days after the CTA showing bleb grwoth he was admitted emergently with a severe SAH (WFNS 5, Fisher 3). The aneurysm was occluded with coils. However, the patient died on day 14 after SAH due to delayed ischemic neurological deficits and multiple organ failure. Conclusions This case illustrates the high rupture risk of an UIA presenting a documented growth of an aneurysm bleb over a short follow-up time. In retrospect, this patient might have benefitted from emergent aneurysm occlusion. The interest of this report comes from the prove that aneurysmal bleb growth constitutes a high risk for short-term aneurysm rupture.