To evaluate the effects of 4 weeks of hand splinting on the length of finger and wrist flexor muscles, hand function, and pain in people with acquired brain impairment.Randomized, assessor-blinded trial.Rehabilitation center in Australia.Twenty-eight adults with acquired brain impairment, all within 6 months of the first injury. There was 1 withdrawal.Subjects in both experimental (n=17) and control (n=11) groups participated in routine therapy-motor training for upper-limb use and upper-limb stretches-5 days a week. The experimental group also wore an immobilizing hand splint in the functional position (10 degrees -30 degrees wrist extension) for a maximum of 12 hours each night for the duration of the 4-week intervention period.The length of the wrist and extrinsic finger flexor muscles was evaluated by measuring the torque-controlled range of wrist extension with the fingers extended. Functional hand use was evaluated with the Motor Assessment Scale. Pain was evaluated with a visual analog scale.The effects of splinting were statistically nonsignificant and clinically unimportant. At follow-up, estimates of treatment effects slightly favored the control group: range of motion at the wrist favored controls by 2 degrees (95% confidence interval [CI], -7.2 degrees to 3.2 degrees ), function favored controls by 0.2 points (95% CI, -2.7 to 2.3), and pain favored the experimental group by 1cm (95% CI, -4.6 to 2.2).An overnight splint-wearing regimen with the affected hand in the functional position does not produce clinically beneficial effects in adults with acquired brain impairment.