We describe the incidence of neurological and psychological side effects after stereotactic thalamotomy in 24 patients with abnormal movements secondary to cerebral palsy. The results of operation are outlined only briefly and, in terms of motor improvement, have been satisfactory. The side effects are categorized as motor or sensory impairments, autonomic disturbances, and mental disturbances. Their frequency and the recovery period are indicated; all of the side effects have been transient. Pathophysiological explanations of these side effects are proposed, correlated with different targets and hemispheric dominance. From our data we can conclude that (a) all side effects after stereotactic thalamotomy are more frequent in patients with cerebral palsy than in other patients and (b) the short time required for the side effects to reverse and their complete remission indicate that they are mainly due to perilesional edema, as suggested by computed tomographic scans.