Objective: To compare the effects of serial casting with positioning for 1 hour per day for the treatment of elbow flexion contracture in adults with traumatic brain injury. Design: Pragmatic randomized controlled trial with concealed allocation and assessor blinding. Setting: Four brain injury rehabilitation units. Subjects: Twenty-six adults with elbow flexion contracture after traumatic brain injury participating in multidisciplinary inpatient rehabilitation. Interventions: Subjects were randomized to receive either serial casting or positioning for two weeks. In the subsequent four weeks subjects could be positioned for up to 1 hour/day. Main measures: Torque-controlled passive elbow extension was measured at baseline, post-intervention (two weeks), post-intervention plus one day, and at follow-up (four weeks post-intervention). Results: All 26 subjects completed the study. Post-intervention, serial casting reduced contracture by an average of 22 degrees (95% confidence interval (CI) 13 to 31; P <0.001) compared with the positioning group. One day later this effect had decreased to 11 degrees (95% CI 0 to 21 degrees; P= 0.052). The effect had almost completely disappeared at the four-week follow-up (mean 2 degrees, 95% CI -13 to 17; P= 0.782). Conclusions: Serial casting induces transient increases in range of motion. These effects are not maintained.