Although there are sound theoretical reasons for the use of botulinum toxin (Btx) as early as possible in the management of severe childhood muscle spasticity, the experience with its safety in children younger than 2 years of age is limited and information about its possible effects on the development and maturation of the human motor system is still scarce. This study discusses the rationale and the potential pitfalls of the use of Btx in the first 2 years of the child's life. It also reviews the currently available evidence on the efficacy and safety of Btx in this age group. It concludes by suggesting a framework for studies of the optimal time to start treatment of childhood spasticity with Btx.