Guidelines have been promoted in various roles in general practice, e.g. to improve quality of care, to assist patient decision making, and to improve resource allocation. This paper examines these claims using ethical analysis. Guidelines may help general practitioners to act for thegood of their patients and avoid harm; but, on their own, guidelines cannot ensure quality of care or the protection of patients' interests. Patient choice may be limited rather than enhanced by following guideline recommendations. Guidelines contribute to rationing of resources but do not use explicit citeria for this. The ethical implications for guideline use are complex and far-reaching