Cerebral Palsy (CP) is a disability that affects more than 100 million children. More than 60% of these children have significant difficulties within their hand abilities, affected by involuntary movements and spasticity. So, to overcome this issue, orthoses are being employed as therapeutic intervention and can allow children with CP to have an opportunity to better use their hands. Three-dimensional (3D) technologies provide the generation of high-quality orthopedic products. Although, there are limited studies related to the evaluation of such assistive devices, especially for children. Therefore, the purpose of this research was to design, develop and evaluate a customized wrist-hand orthosis using 3D technologies for a child with CP. So, it was used a high-level 3D scanning to acquire the wrist-hand anatomy, a free software for 3D modelling and a low-cost 3D printer for manufacturing the orthosis. The Jebsen-Taylor Test of Hand Function (JTTHF) was used to evaluate unilateral hand abilities. We noticed improvements while wearing the orthosis at the affected hand, in the following subtests: writing (13 s), lifting small objects (0.9 s) and simulated feeding (69.3 s). The customized orthosis was able not only to improve some functional hand skills, but also to provide comfort, better fitting and with an appealing aesthetic design.