Introduction: The overall prevalence of unruptured intracranial aneurysms is 3.2%. The rupture risk of an intracranial aneurysm during cardiopulmonary bypass requiring full heparinisation is unknown. Patients and Methods: Rupture risk was assessed using data from a trial in which dexamethasone was compared with placebo in 4482 patients undergoing cardiac surgery with cardiopulmonary bypass. Results: Not a single haemorrhagic stroke occurred during surgery and only one patient had a subarachnoid haemorrhage three weeks after cardiac surgery. Discussion: Although the actual prevalence of intracranial aneurysms in the study population is unknown, based on patient characteristics, it is likely that the incidence is not below the average of 3.2% of the general population. So probably at least 143 patients with an intracranial aneurysm underwent surgery with full heparinisation without any rupture. Conclusion: Cardiopulmonary bypass with heparinisation is not a risk factor for rupture of an intracranial aneurysm. An unruptured intracranial aneurysm should not hinder lifesaving surgery for which cardiopulmonary bypass is required. © 2018 NVIC. All rights reserved.