The assessment of walking in children affected by cerebral palsy (CP) is currently based principally on qualitative assessment criteria. Gait analysis, meanwhile, evaluates quantitatively kinematic and dynamic aspects of locomotion. The main aim of this study was to examine (using an optoelectronic system and a force platform) kinematic and dynamic aspects of the ankle joint in hemiplegic and in diplegic children (9 and 11 subjects respectively) and in 10 normal control subjects. Our results reveal, in spastic subjects, "equinus" placement of the foot in the initial contact phase, a lack of dorsiflexion (negative DF peak) in the stance phase and a reduction in push-off capacity (capacity to move the leg forward) in the swing phase. The results furnished by this study represent a useful contribution to the assessment of the walking ability of children affected by CP and to the evaluation of the indications and advantages of the rehabilitative intervention chosen.