An up-to-date overview regarding functional outcome measures, which are factors within clinical diagnostics and treatment of children and adolescents with OI, and the influence of medication on their functional outcome will be given in this chapter, in which the ICF-CY could serve as a conceptual model. All functional outcome measures described in this chapter are divided in three categories: (1) body function and structure, (2) participation and activities and (3) outcome measures and utilized instruments. Furthermore, the role of intervention and physical training, next to perspectives for current and future clinical diagnostics and treatment strategies within the domain of functional outcome are described and discussed.