The purpose of this study was to compare the effectiveness of balance training using the Biodex balance system and a conventional balance training programme on balance score and on gross motor skills of children with spastic diplegia.A randomized controlled study was conducted on 48 spastic diplegic children with cerebral palsy (26 boys and 22 girls) in the age range of 5-8 years. The children were randomly allocated to two equal groups. The investigators performed balance and gross motor function assessments for every child using the paediatric Berg balance scale and the gross motor function measure -88 scale (dimensions D and E) before and after the treatment programme. Passive repositioning sense was measured by a Biodex III isokinetic dynamometer. The study group received Biodex balance training and traditional physical therapy programme training, whereas the control group received conventional balance training in addition to the traditional physical therapy programme training, 3 times per week for 12 weeks.Significant improvement was observed in all outcome measures of the two groups, comparing their pre- and post-treatment mean values. Furthermore, the results revealed a significant (P < 0.05) improvement in mean post-treatment values for the Biodex balance training group.Balance training using the Biodex balance system is superior to conventional balance training for improving the balance abilities and gross motor functions of children with cerebral palsy and spastic diplegia.