BACKGROUND: Hip arthroscopy can be performed with the patient in the lateral or supine position, but it remains technically demanding. We aimed to objectively quantify and compare learning curves between two groups of orthopaedic trainees randomized to learn simulated hip arthroscopy with the patient in either a lateral or a supine position. We also compared learning curves between senior and junior trainees. METHODS: A hip arthroscopy simulator with anterolateral and anterior portals, a 70° arthroscope, and fixed distraction was used. Rotation of the simulator by 90° enabled arthroscopy with the patient in a supine or lateral position. Twenty orthopaedic trainees with minimal hip arthroscopy experience were randomized into lateral and supine position groups, and were asked to perform a diagnostic hip arthroscopy of the central compartment on twelve occasions. Each episode involved a change in the portal and repetition of the diagnostic round. A validated motion analysis system objectively measured surgical performance by recording time taken, total path-length of the hands, and number of hand movements. RESULTS: Both groups demonstrated learning with objective improvement in all parameters (p