OBJECTIVE: To investigate the co-ordination between reaching, ground reaction forces and muscle activity in standing children with severe spastic diplegia wearing dynamic ankle-foot orthoses compared with typically developing children. DESIGN: Clinical experimental study. SUBJECTS: Six children with spastic diplegia (Gross Motor Function Classification System level III-IV) and 6 controls. METHODS: Ground reaction forces (AMTI force plates), ankle muscle activity (electromyography and displacement of the hand (ELITE systems) were investigated while reaching for an object. RESULTS: For the children with severe spastic diplegia who were wearing dynamic ankle-foot orthoses, co-ordination between upward and forward reach velocity differed regarding the temporal sequencing and amplitude of velocity peaks. During reaching, these children lacked interplay of pushing force beneath the reach leg and braking force beneath the non-reach leg and co-ordinated ankle muscle activity, compared with controls. CONCLUSION: The results suggest differences in reach performance and postural adjustments for balance control during a reaching movement in standing between children with spastic diplegia Gross Motor Function Classification System level III-IV, wearing dynamic ankle-foot orthoses compared with typically developing children.