Objective. To establish the effect of a game-based exercise programme on Physical Deconditioning Syndrome (PDS) in 5 to 12 year-old children suffering Acute Lymphocytic Leukaemia (ALL). Materials and methods. This was a quasi-experimental study involving seven children being treated for ALL at the National Cancer Institute (NCI) in Bogotá, Colombia. Fitness determinants (aerobic capacity, muscle strength, flexibility, motor skills and proprioception) were initially assessed to establish their exercise regime category, classifying subjects into three levels. Post-intervention assessment at the end of the programme verified changes in such determinants. Results. Seven children aged 5 to 12 years-old (9±2.13 years) suffering from ALL (4 girls and 3 boys) met the inclusion criteria. Most determinants underwent changes leading to an increase in patients’ evaluation scores (except for muscle strength, which remained constant). Whilst determinant variation was important, a greater difference was found when the overall score was analysed (p=0.05), signifying that the intervention had changed these children’s health status. Conclusion. Game-based exercise was useful for managing PDS in 5 to12 year-old ALL patients and suggested new ways of providing an intervention concerning physical therapy. However, studies involving a larger target population and longer intervention time are needed to identify new findings in this field.