We assessed decision making in 20 patients newly diagnosed with obstructive sleep apnoea (OSA) and 20 healthy controls with the Iowa Gambling Task (IGT), which evaluates the ability to learn to sacrifice immediate rewards in favour of long-term gains. A standard neuropsychological battery was administered. Switching scores tended to be lower in patients. Patients persisted in selecting risky decks throughout the IGT, whereas controls behaved normally. Performance was correlated with hypoxaemia. Brain regions underlying decision making may be affected by OSA-related hypoxaemia.