This paper investigates how the increased rate of Quality and Outcomes Framework (QOF) payments implemented on 1 April 2005 affects Scottish general practitioners’ (GPs) intrinsic, extrinsic and overall motivation. A first difference method is used to model GPs’ intrinsic and overall motivation. The main finding is that the increased QOF payment effectively motivated GPs’ health care supply, but it also ‘crowded out’ GPs’ intrinsic motivation. The result suggests that using strong financial incentives to further motivate already well-motivated health care professionals may have unintended effects on their performance.