Patients with aneurysmal subarachnoid haemorrhage (SAH) secondary to ruptured anterior communicating artery aneurysms (ACoA) often suffer from neuropsychological sequelae including personality and behavioural changes. In this study, 31 patients with ruptured aneurysms of the ACoA resulting in SAH [mean age 50.9 years, NART (National Adult Reading Test) IQ 108.7] were compared with a group of 29 normal controls (mean age 51.9 years, NART IQ 109.7) on a specific task of decision-making. A similar task has been imaged previously and shown to activate regions involving the ventromedial prefrontal cortex. Patients with ACoA rupture showed no significant difference from controls on the task in their speed or quality of decision-making. They did, however, exhibit increased risk-taking behaviour, placing higher bets in a measure of the task which involved choices between actions associated with differing magnitudes of reward and punishment. ACoA patients demonstrated true risk-taking behaviour as opposed to simple impulsivity. Such a deficit in decision-making may be a result of direct damage to the orbital prefrontal cortex itself (as a result of micro-ischaemia or infarction after ACoA aneurysmal rupture) or to a disconnection in the ventromedial circuits from distant or generalized brain damage.