Background: Current research mainly employs cross-sectional designs to examine changes in medical students' attitudes towards complementary and alternative medicine (CAM). Aims: This paper reports the findings of a longitudinal study to further validate the Integrative Medicine Attitude Questionnaire (IMAQ) and examine changes in medical students' attitudes over 3 years. Methods: Atotal of 154 medical students from four schools in three countries completed a modified version of the IMAQ during their first (T1) and fourth year (T2). Results: We established the validity of a three-factor model for the IMAQ: (1) attitudes towards holism; (2) attitudes towards the effectiveness of CAM therapies, and (3) attitudes towards introspection and the doctor-patient relationship. We found that IMAQ factor scores did not differ significantly from T1 to T2, emphasizing the relative stability in attitudes across time. Various student characteristics were significantly associated with IMAQ factor scores at T2: age, gender, CAM use, CAM education and school; and two variables (gender and CAM use) predicted changes in medical students' attitudes between T1 and T2. Conclusions: We urge medical educators to continue exploring medical students' attitude changes towards CAM and we provide examples of what further research is needed.