BACKGROUND Although botulinum toxin A is frequently used to augment serial casting in the treatment of soft-tissue contractures in children with cerebral palsy, its effectiveness for this purpose has not been evaluated. The purpose of the present study was to determine whether botulinum toxin A injection increases the efficacy of serial casting. METHODS A prospective, randomized trial was undertaken to compare serial casting only with serial casting combined with botulinum toxin A (Botox) injection for the treatment of ankle equinus contractures in twenty-three children with cerebral palsy. Range-of-motion testing, spasticity assessment, and computerized gait analysis were performed as long as twelve months after treatment. RESULTS There was no difference between the groups with regard to the duration of casting required to correct the equinus contracture. Both groups maintained a significant improvement in passive ankle dorsiflexion throughout the follow-up period, although the group managed with casting and Botox had a significant loss of dorsiflexion when the values at six, nine, and twelve months were compared with the value at three months. Peak dorsiflexion during the stance and swing phases was significantly improved in both groups at three months but only in the group managed with casting alone at twelve months. Plantar flexor spasticity was significantly decreased at three months in both groups, but it was significantly decreased at six, nine, and twelve months only in the group managed with casting alone. Spasticity was significantly greater in the group managed with casting and Botox than it was in the group managed with casting only at six, nine, and twelve months. CONCLUSIONS The present study demonstrates the efficacy of serial casting in the treatment of equinus contractures in children with cerebral palsy who are able to walk. Contrary to our hypothesis, the addition of botulinum toxin A to a serial casting regimen led to earlier recurrence of spasticity, contracture, and equinus during gait. The results of the present study suggest that botulinum toxin combined with serial casting for the treatment of fixed contractures will lead to a recurrence of plantar flexor spasticity and equinus contracture by six months in this patient population. While previous research has indicated that the injection of botulinum toxin A is superior to casting for the treatment of dynamic equinus, the present study suggests that serial casting alone is preferable for the treatment of fixed equinus contractures in children with cerebral palsy.