What is already known on this topic * Cost containment through the most effective mix of staff achievable within available resources and organisational priorities is of increasing importance in most health systems. However, there is a dearth of information about the full economic implications of changing skill mix. * In the UK a major shift in the primary care workforce is likely in response to the rapidly developing role of nurse practitioners and policies aimed to encourage GP practices to transfer some of their responsibilities to other, less costly, professionals. * Previous research has developed an approach to incorporating the costs of qualifications, and thus the investment required to develop a skilled workforce, for a variety of health service professionals including GPs. What this study adds * This paper describes a methodology of costing nurse practitioners that incorporates the human capital cost implications of developing a skilled nurse practitioner workforce. With appropriate sources of data the method could be adapted for use internationally. * Including the full cost of qualifications results in nearly a 24 per cent increase in the unit cost of a Nurse Practitioner. * Allowing for all investment costs and adjusting for length of consultation, the cost of a GP consultation was nearly 60 per cent higher than that of a Nurse Practitioner.