Our aim was to examine the feasibility and effects of robotic therapy for children with cerebral palsy and upper limb hemiplegia. A single group within-subjects design was used. Twelve children aged 5-12 yrs with moderate to severe motor impairments participated in 1-hr robotic therapy sessions, 2 times per week for 8 wks. During each session, children used the paretic arm to perform 640 repetitive, goal-directed planar reaching movements, with robotic assistance as needed. Primary outcomes were the Quality of Upper Extremity Skills Test (QUEST) and the Fugl-Meyer Assessment upper limb subtest. Secondary outcomes were the Modified Ashworth Scale, peak isometric strength of shoulder and elbow muscles, and parent questionnaire scores. We found significant gains in total QUEST and Fugl-Meyer Assessment scores at discharge and follow-up and in isometric strength of elbow extensors at discharge. The parent questionnaire showed significant improvements in "how much" and "how well" children used the paretic arm during daily functional tasks at home. Robotic therapy can provide new opportunities for improving upper limb coordination and function in children with moderate to severe impairments due to cerebral palsy or stroke.