Aim: The objective of this study was to assess the reliability of a mobility questionnaire (MobQues) that was developed to measure the mobility limitations of children with cerebral palsy (CP) as rated by their parents. A clinical version of the questionnaire, consisting of 47 items (MobQues47), is available, as well as a research version with 28 items for a specific population (MobQues28). Total scores are expressed on a scale of 0 to 100. Method: We assessed the interrater reliability between both parents of 289 children with CP (168 males, 121 females, age range 2-13y, Gross Motor Function Classification System levels I-IV) and the intrarater reliability within a subgroup of 38 parents (of 23 children) who completed the MobQues twice. Results: For the interrater reliability, high intraclass correlation coefficients (ICCs) were found for the MobQues47 (ICC 0.92) and MobQues28 (ICC 0.87). The standard error of measurement (SEM) was 7.8 and 8.9 respectively. As expected, the intrarater reliability was higher, as represented by higher ICCs (0.96-0.99) and lower SEMs (3.5-4.9) for both MobQues versions. Interpretation: The results of this study indicate that the MobQues is a reliable instrument to measure the mobility limitations of children with CP. © The Authors. Journal compilation © Mac Keith Press 2009.