The present study was performed to assess dose-response relationships of local botulinum toxin A (BtxA) treatment in children and teenagers with spastic gait due to cerebral palsy (CP) in a randomized, double-blind study employing a "high-dose" (200 units Botox per leg) and a "low-dose" (100 units Botox per leg) treatment arm in 33 patients with CP. Response parameters included changes in muscle tone assessed by the Ashworth scale at knee joint, range-of-motion (ROM) measurements at knee and ankle joint, objective analysis of longitudinal gait parameters as well as subjective assessments of improvement. Patients in the "high-dose" arm received 40-80 units Botox/muscle versus 20-40 units Botox/muscle in the "low-dose" group. Patients in both treatment arms showed significant improvement of Ashworth score (p<0.001) and ROM (p<0.01), while gait analysis revealed significant increase in gait velocity (p<0.01) and stride-length (p<0.001) over baseline. Subjects in the "high-dose" group showed significantly greater improvement on objective response measurements compared to "low-dose" patients. Also, children aged 7 years or less had greater functional benefit compared to the subgroup of patients older than 7 years. Incidence and severity of side-effects were similar in both treatment groups. The present study demonstrated dose-dependent functional improvement of dynamic deformities and spastic gait pattern in children and young adults with CP treated with local injections of botulinum toxin. A dose of 200 units Botox per leg distributed to 4 or 5 muscle bellies per leg is superior compared to 100 units Botox per leg without significantly affecting the risk of side-effects.