Studies of lesions of the primate cerebellum leave little doubt that the cerebellum is necessary for the execution of smooth and accurate movements. How the cerebellum fulfills this role at a neuronal level remains unknown. It is likely that the cerebellum exerts the same effect on a number of different efferent targets. In order to influence voluntary movement, a major output from the cerebellum projects to the motor cortex via the cerebello-thalamo-cortical (CTC) pathway. By examining neuronal activity in the cerebellar thalamus, and comparing this with activity recorded from its connections with the deep cerebellar nuclei and motor cortex, conclusions can be made regarding cerebellar function. Current data does not support a role for the CTC pathway in the initiation of movement or the control of trans-cortical reflexes. Also, the evidence does not support the hypothesis that the cerebellum prevents terminal movement oscillations by predictively sending a message to the antagonist muscle to brake the movement. The available literature supports the Eccles theory that during normal movement, the CTC pathway receives a form of efference copy from the motor cortex and compares this message with that derived from peripheral afferents about the actual progress of the movement. However, there is not a significant degree of kinematic information passing through this pathway in the course of a voluntary movement. Therefore the actual site of comparison or error-detection in this system awaits further elucidation.