AIM: Botulinum toxin A (BoNT-A) combined with occupational therapy is effective in improving upper limb outcomes in children with unilateral cerebral palsy (CP). It is now essential to identify the most effective therapies following BoNT-A. Given the added burden for children and families, the aim of this study was to explore whether modified constraint-induced movement therapy (mCIMT) leads to sufficiently superior gains compared with bimanual occupational therapy (BOT) in young children with unilateral CP following BoNT-A injections. METHOD: In this randomized, controlled, evaluator-blinded trial, 34 children (20 males, 14 females; mean age 3y, SD 1y 4mo, range 18mo-6y) with unilateral CP were randomized using concealed allocation to one of two 8-week interventions. The experimental group (n=17) received BoNT-A and mCIMT. The comparison group (n=17) received BoNT-A and BOT. Participants were recruited from a physical rehabilitation clinic and randomized between August 2003 and May 2009. Primary outcome was measured using the Assisting Hand Assessment at 3 months. Secondary outcomes were measured at 3 months and 6 months using the Quality of Upper Extremity Skills Test, the Pediatric Evaluation of Disability Inventory, Canadian Occupational Performance Measure, and the Goal Attainment Scale. RESULTS: There were no clinically important differences between groups at baseline. Immediately following intervention, there was no evidence of a superior effect for BoNT-A + mCIMT as determined by the Assisting Hand Assessment (estimated mean difference [EMD] 0.81, upper 95% confidence limit 3.6; p=0.32) or secondary outcomes. However, both groups showed improvement over time (BoNT-A + mCIMT: EMD 2.7, 95% confidence interval [CI] 0.7-5.2; BONT-A + BOT: EMD 4.7, 95% CI 2.1-8.6). Follow-up at 6 months also demonstrated no superior effect for BoNT-A + mCIMT. INTERPRETATION: Following upper limb injection of BoNT-A, there was no evidence that mCIMT, despite the significantly increased intensity of the home programme, produced a superior effect across a range of outcomes compared with a structured programme of BOT in young children with unilateral CP.