<p><strong>Background:</strong> Hydrotherapy according to Halliwick concept is a physiotherapeutic intervention technique for disabled patients and for children with neurodevelopmental disorders. Assessing the balance in children with cerebral palsy (CP) is an extremely complex process and more difficult to evaluate the results of some therapeutic interventions in these patients. The purpose of this study is to investigate the effect of Halliwick based Hydrotherapy on the support base in children with CP. Several studies have proven the beneficial effects of hydrotherapy in the respiratory system of children, but few are studies that report the effect on the balance of children with CP.</p><p><strong>Methods:</strong> The study involved 16 children diagnosed with CP. The 10 children were following a Halliwick Concept hydrotherapy program and the 6 children classical physiotherapy program for 3 months. Their balance was assessed with the Berg, GMFM, and footprint plate. The assessment was performed at the start of the program (pre-test) and after 3 months (post-test).</p><p><strong>Results</strong>: Τhere is a statistically significant change between the 1<sup>st</sup> and 2<sup>nd</sup> measurement with the BERG and GMFM tools and better for the water intervention group. The change in the support base between the 1st and 2nd measurement was better in the water intervention group but not statistically significant.</p><p><strong>Conclusions:</strong> The results of the study showed that hydrotherapy according to Halliwick has positive effects on gross mobility and the balance of children with CP. It also appears to have a positive effect on changing the support base compared to classical physiotherapy.</p>