Muscle overactivity is common in patients with adult onset central nervous system damage. It can produce significant disablement in conjunction with other impairments such as adaptive soft tissue shortening and loss of muscle strength. Muscle overactivity is not evenly distributed throughout the body; across joints there is frequently imbalance between agonist and antagonist, producing abnormal joint postures and movement patterns. Due to the asymmetric nature of the abnormal activity across joints, in general we recommend local treatment targeting the more overactive of the two agonists, rather than systemic treatment. Considerable experience with the use of botulinum toxin, both serotypes A and B, in the treatment of muscle overactivity has been accumulated in the last two decades through pragmatic clinical practice and open label studies, supported by an increasing number of randomized controlled trials. In most cases, it is important to use botulinum toxin injection for treatment of muscle overactivity in the setting of wider rehabilitation goals and interventions. Focal and partial blocks with botulinum toxin should be used as a component of a general neurorehabilitation programme rather than as an alternative to other treatments. We review the evidence supporting the use of botulinum toxin to treat muscle overactivity in the lower limb, present practical guidelines on when and how to use botulinum toxin and provide direction for future research.