Background: Curricula are accommodated to the interests of new groups after pressure from social movements outside institutions. A Dutch national project to integrate gender-gender mainstreaming (GM)-in all medical curricula started in 2002 and finished in 2005. GM is a long-term strategy which aims at eliminating gender bias in existing routines for which involvement of regular actors within the organization is required. Aims: In this paper, the challenges of GM in medical education are discussed. Three case studies of medical schools are presented to identify key issues in the change process. Method: Steps taken in the national project included the evaluation of a local project, establishing a digital knowledge centre with education material, involving stakeholders and building political support within the schools and national bodies, screening education material and negotiating recommendations with course organizers, and evaluating the project with education directors and change agents. Data are gathered from interviews and document analysis. Results: Factors playing a role are distinguished at three levels: (1) policy level, such as political support and widespread communication of this support; (2) organizational level such as a problem-based curricula and procedures for curriculum development and evaluation; and (3) faculty's openness towards change in general and towards feminist influences in particular, and change agents' position as well as personal and communicative skills. Conclusions: Successful GM in medical education is both a matter of strategy as well as how such strategy is received in medical schools. A time-consuming strategy could overcome resistance as well as dilemmas inherent in GM. More female teachers than male teachers were openly accepting. However, women were situated in less visible and less powerful positions. Hence, GM is accelerated by alliances between women aiming for change and senior (male) faculty leadership.