Patients with focal dystonia exhibit proprioception abnormalities that can lead to kinematic deficits. Proprioceptive abnormalities are present in both symptomatic and asymptomatic body parts of dystonic patients. To ascertain whether in patients with idiopathic cervical dystonia (CD) movements performed with nondystonic segments display kinematic abnormalities, we studied trajectory formation of out and back arm reaching movements in 10 patients with CD (before and 3 weeks after treatment with Botulinum toxin) and in 10 age-matched controls. Before treatment, patients with CD showed significant trajectory abnormalities when compared with normal controls. Patients' trajectories were more curved with asymmetrical temporal velocity profiles as well as increased hand path areas, and had longer reversal lags between the out and back segments. Treatment with botulinum toxin improved all the kinematic parameters. These results suggest that in patients with CD, movements performed with nondystonic segments are abnormal. The kinematic abnormalities are likely to derive from long-standing defective integration of the proprioceptive input, which, in turn, causes general changes in the internal models of limb dynamics. It is plausible that treatment with botulinum toxin partially restores proprioceptive processing and thus, such internal models.