Purpose: To determine the feasibility of conducting a definitive randomised trial to evaluate the efficacy of custom-fitted footwear for increasing physical activity in children and adolescents with Down syndrome.Methods: Assessor-blinded, parallel-group randomised pilot study. Thirty-three children and adolescents with Down syndrome were randomly allocated to a custom-fitted footwear group (Clarks® footwear) or a wait-list control group. Six feasibility domains were evaluated at baseline, 6 and 12 weeks; demand (recruitment), implementation (co-interventions and adherence), acceptability, practicality (adverse events), limited efficacy testing (physical activity, disability associated with foot and ankle problems, and gait parameters), and adaptation (shoe-fit).Results: Three participants were recruited per month. The use of co-interventions was common with six control group participants purchasing new footwear during the study. Mean adherence was 35 h/week in the custom-fitted footwear group, and there were few minor adverse events. There were trends for differences in physical activity favouring the custom-fitted footwear, but no trends for differences in disability associated with foot and ankle problems or gait parameters. The fit of the custom-fitted footwear was no better than participants' regular footwear.Conclusions: A definitive randomised trial is feasible. However, recruitment, use of co-interventions and footwear fit need further consideration.Implications for rehabilitationConducting a definitive randomised trial to determine the efficacy of custom-fitted footwear in increasing physical activity in children and adolescents with Down syndrome is feasible.Custom-fitted footwear may improve physical activity in children and adolescents with Down syndrome.Commercially available footwear may not be suitable for children and adolescents with Down syndrome due to their unique foot shape.