Pay for performance, or “P4P” as it is often known, is now centre-stage in primary care in the United Kingdom. P4P promotes change in clinical behaviour by offering financial rewards in return for achieving certain predefined targets. Both sides of the P4P “equation” are currently the subject of much debate: how generous should the financial reward be (the first “P”); and which performance indicators (the second “P”) should be used as the basis for calculating eligibility for the reward?