Objective: To develop a Rasch-based version of a mobility questionnaire (MobQues28) for children with cerebral palsy (CP). Design Cross-sectional study. Setting Private physical therapy practices and outpatient departments of hospitals and rehabilitation centers. Participants Parents of 323 ambulatory children with CP (Gross Motor Function Classification System [GMFCS] level I-IV; aged, 213y). Interventions Not applicable. Main Outcome Measure The mobility questionnaire measures mobility limitations in children with CP by rating the difficulty of executing 47 mobility activities, as reported by the parents. Items for the Rasch-based version were selected based on fit to the Rasch measurement (partial credit) model and invariance of item characteristics across GMFCS level, age group, or sex. Results Analysis revealed a fitting model when nonambulant and/or 2- and 3-year aged children were excluded (leaving a final sample of n=246) and answering categories were collapsed from 9 to 5. Thirteen items were removed from the questionnaire due to misfit to the model, 5 because of disordered thresholds, and 1 because of invariance across age group. Twenty-eight items out of the original 47 items showed good fit to the model. Conclusions The 28-item version of the mobility questionnaire (MobQues28) provides sound measurement properties for measuring mobility limitations in ambulant children with CP, aged 4 to 13 years, and shows promise as an instrument for research purposes. © 2011 American Congress of Rehabilitation Medicine.