To quantify the angle of movement, distance travelled, and center-of-gravity (CoG) shift in each body part, and clarify compensatory movements when patients with spastic diplegia perform a reach. [Participants and Methods] Seven patients with spastic diplegic cerebral palsy and 8 healthy adults performed a reach as a task to measure the time needed to reach, distance travelled, angle of movement, and CoG sway. [Results] The distances travelled forward by the lower trunk and pelvis were shorter, and those travelled by the upper limb and upper trunk were longer in patients with spastic diplegia compared with healthy adults. Furthermore, in the former group, the maximum amplitude of sway was smaller, and its velocity was slower in the anteroposterior direction. [Conclusion] As compensatory movements for reaching in patients with spastic diplegia, the degree of anterior pelvis tilt is reduced, and the shoulder girdle and upper limb with higher mobility are excessively moved forward. During these movements, the trunk is fixed by excessive upper trunk flexion and neck extension.