Two studies tested self-determination theory with 2nd-year medical students in an interviewing course. Study 1 revealed that (a) individuals with a more autonomous orientation on the General Causality Orientation Scale had higher psychosocial beliefs at the beginning of the course and reported more autonomous reasons for participating in the course, and (b) students who perceived their instructors as more autonomy-supportive became more autonomous in their learning during the 6-month course. Study 2, a 30-month longitudinal study, revealed that students who perceived their instructors as more autonomy-supportive became more autonomous in their learning, which in turn accounted for a significant increase in both perceived competence and psychosocial beliefs over the 20-week period of the course, more autonomy support when interviewing a simulated patient 6 months later, and stronger psychosocial beliefs 2 years later.