The ability to reflect on one's own action is seen as an important skill for a doctor. A thorough introduction of the portfolio planned in the early stages of their studies seems to be the way to train medical students in reflection. This article describes the use of portfolios in early undergraduate medical training. The literature on portfolios suggests three aspects that are crucial for the effectiveness of portfolios: structure, coaching and assessment. The portfolio system was designed by transposing the experience with portfolio systems outside and inside medical training to a situation of first-year medical students. During the academic year 2001-02 242 first-year medical students compiled a portfolio. Student experience was collected by semi-structured interviews. The majority of students were of the opinion that analysing one's competences in a portfolio was instructive and meaningful. With regard to learning how to reflect and recognize learning needs, however, mentor coaching proved to be necessary. The results thus far show that the portfolio is a worthwhile addition to existing assessment and learning tools.