The aim of this study was to evaluate the effect of therapeutic electrical stimulation (TES) applied to antagonists of spastic leg muscles on gross motor function in children with spastic diplegic cerebral palsy. Twelve children between 5 and 12 years of age completed a 24-month crossover study in which six were randomly assigned to receive TES for the first 12 months and the remaining six for the last 12 months. Physiotherapy and a home training program were not altered. All were evaluated blindly in terms of tests of motor function and video recordings at the start and at 12 and 24 months. At the end of the study parents/carers gave a subjective assessment of the effect of TES. No significant effect of TES on motor or ambulatory function was found on the blinded evaluation, but parents of 11 of the 12 children stated that TES had a significant effect. We conclude that it is unlikely that TES has a significant effect on motor and ambulatory function in spastic diplegia.