Bilateral spastic cerebral palsy (BSCP) patients frequently need to use various sitting devices for body control and function. The aim of this study was to investigate whether the use of a belt to position the pelvis in an adjustable chair would affect upper limb function in preschool children with BSCP. Forty-one children with BSCP [mean age 44 +/- 11, range 18-60 months] classified according to the Gross Motor Function Classification System (GMFCS), as level III (n=21) and level IV (n=20) were fitted with a hip-positioning belt. Upper limb functions were assessed by Quality of Upper Extremity Skills Test (QUEST). The median scores of the following upper extremity functions increased significantly by wearing the hip positioning belt: dissociated movements, grasping, weight bearing and protective extension. The total QUEST score increased from 56.7 (+/- 46.3) to 66.1 (+/- 39.2) (p<0.001). The portable and adaptable hip-positioning belt may be used in daily life to improve upper limb activity in preschool children with moderate to severe BSCP.