Cerebral Palsy (CP) is a permanent condition and is the most common cause of significant physical disabilities and motor impairment in childhood. The Surveillance of Cerebral Palsy in Europe (SCPE) network indicates an overall prevalence of CP in Europe of 0.89, 6.2, 35.9, and 38.2 for normal, moderately low, very low and extremely low birthweight children, respectively, per 1000 live births. The number of patients is expected to increase as the risk of developing CP is higher in premature children, who nowadays have an increased survival rate. In Portugal, the last report from the National Surveillance of PC at 5 years old refers an annual incidence of 2 cases per 1000 live births. Children with CP suffer from a brain lesion which results in impaired motor control, spasticity and muscle weakness (primary disorders) and contractures and lower limb bone deformities (secondary disorders). These factors undermine gait performance and mobility, being an obstacle to the integration, inclusion and participation of these children in the society. This condition involves high costs both for the child and their family and for the national healthcare system. The complexity of this condition demands a transdisciplinary support system through life, involving clinical, social security and educational components. To improve gait performance, children with CP are often treated with single event multi-level surgery (SEMLS), usually in association with localized botulinum toxin injections (BTI). SEMLS is an invasive procedure with permanent outcomes, the BTI is less invasive but the outcomes are only temporary. Currently the type of treatment (BTI or SEMLS) and its patient-specific adjustment are based on a clinical assessment of the patient, integrated 3D clinical gait analysis (CGA) and the experience of the clinical staff. CGA has drastically helped the clinical decision making process in developed countries. However functional outcomes are not always easy to predict, resulting in unwanted follow-up treatments. This is mainly due to the difficulty to predict gait functional outcome, since gait performance relies on a complex interaction between musculoskeletal geometry, muscle weakness, increased muscle-tendon stiffness and impaired motor control. The use of accurate subject specific musculoskeletal computer simulations (SS-MSK) of the treatment could help to predict its outcomes and thus further assist the clinical decision making process. Determining the amount of clinical data that is crucial to allow a valid simulation of the intervention results, so that the use of SS- MKS become more cost effective will be crucial. By predicting gait performance in each child with CP, the risks of the intervention can be quantified, and each intervention can be fine-tuned. Consequently, unnecessary surgeries can be avoided, decreasing the social and economic costs, as well as unwanted surgical outcomes that can be expensive for the families and for the child well-being.