The role of the flipped classroom model in graduate medical education (GME) is not yet defined. We set out to evaluate the feasibility, acceptability and outcomes of a flipped classroom instructional model in an internal medicine curriculum.This pilot study was carried out in an academic medical centre in the USA with 43 second-year internal medicine postgraduate trainees. Trainees watched videos on the pharmacological treatment of type 2 diabetes outside of the classroom, followed by an in-class session in which they engaged in case-based discussions. The intervention was evaluated using surveys and a knowledge test before, immediately after and 6 months after the intervention.The mean number of correct answers for a 10-question knowledge test was 5.25 before the intervention, 8.00 in the immediate post-intervention test, and 7.10 in the 6-month follow-up test (p < 0.001). Six months after the intervention, 57.1% of participants reported prescribing an antidiabetic medication discussed at the session. In a focus group, trainees reported their preference for interactive, case-based learning, concern about the time required for preparation and interest in incorporating real patient cases.Trainees preferred the flipped classroom, which also resulted in increased knowledge and self-reported prescribing changes; however, the required preparatory time may limit its feasibility in GME.