This study investigated interrater reliability and measurement error of the Melbourne Assessment of Unilateral Upper Limb Function (Melbourne Assessment) and the Quality of Upper Extremity Skills Test (QUEST), and assessed the relationship between both scales in 21 children (15 females, six males; mean age 6y 4mo [SD 1y 3mo], range 5-8y) with hemiplegic CP. Two raters scored the videotapes of the assessments independently in a randomized order. According to the House Classification, three participants were classified as level 1, one participant as level 3, eight as level 4, three as level 5, one participant as level 6, and five as level 7. The Melbourne Assessment and the QUEST showed high interrater reliability (intraclass correlation 0.97 for Melbourne Assessment; 0.96 for QUEST total score; 0.96 for QUEST hemiplegic side). The standard error of measurement and the smallest detectable difference was 3.2% and 8.9% for the Melbourne Assessment and 5.0% and 13.8% for the QUEST score on the hemiplegic side. Correlation analysis indicated that different dimensions of upper limb function are addressed in both scales.