We report a case of subarachnoid haemorrhage resulting from a mycotic aortic aneurysm in a child with CHD. The patient previously underwent operations for CHD and had a subarachnoid haemorrhage of unknown cause before the scheduled re-operation. During the re-operation, a sealed rupture of an undiagnosed mycotic ascending aortic aneurysm was identified, and the causative organism was later identified as Streptococcus. A postoperative MRI indicated a partially thrombosed cerebral aneurysm. This case demonstrates that a mycotic aortic aneurysm can be a cause of intracranial haemorrhage in children.