In three experiments with graphical tasks we examined whether the decreased movement speed in girls with Turner Syndrome (TS) is caused either by a diminished planning capacity or by more peripheral motor execution problems. Fourteen girls with TS and 14 matched controls (mean age 11.6 years) participated. Task difficulty addressed the muscle-initiation, size control, and shape-programming level (Van Galen, 1991). The influence of task difficulty on accuracy, velocity, velocity profile and dwell time was analyzed and confirmed that girls with TS do not plan and program their movements differently from normals. We conclude that the decreased movement speed in TS is caused by problems at the muscle initiation level.