The use of botulinum toxin in cerebral palsy is still experimental. We conducted a pilot clinical trial with botulinum toxin injections on 14 children with spastic cerebral palsy. All patients were mobile with dynamic contractures of the gastrocnemius-soleus muscles. The injections were monophasic in 9 patients and biphasic in 5 patients. Improvement in dorsiflexion, quality of gait and grade of independence were achieved in 3 patients; improvement in dorsilflexion and quality of gait were achieved in 6 patients. There was no significant change in quality of gait in 4 patients. The beneficial effect lasted 4-9 months (mean 6.7 months). A combined functional score given by the physicians, therapists and parents showed a marked improvement in 6 patients (42.9\%), a mild improvement in 3 patients (21.4\%) and no improvement in 5 patients (35.7\%). Biphasic injections were slightly more effective than monophasic injections (p < 0.02). Adverse effects were usually mild. We conclude that botulinum toxin may be used for the reduction of spasticity in patients with cerebral palsy who have dynamic deformities of the ankle joints.