A prospective long-term semiquantitative evaluation of the results of ventral intermediate-posterior ventral oral nucleus thalamotomy on the different aspects of dystonia was made in 29 patients with secondary disease, 12 with nonfamilial, eight with (non-Jewish) familial, and seven with atypical DMD. The effect of disease progression, even in secondary patients, on surgical outcome was reviewed. Thalamotomy resulted in a long-term improvement in limb function of more than 25% to 50% in 23% of the patients, over 50% in 34% of patients, but midline features responded poorly. Manual dexterity was little changed in secondary cases because of underlying paralysis but improved 38% in cases of DMD. Involvement of neck and trunk, of three to four limbs, and progressive disease prognosticated for a poorer result, but phasic and tonic, familial, and nonfamilial dystonia respond equally well and age at surgery made no difference. Significant complications in 29 secondary cases included one death 31 days postoperative, one case of worsened hemiparesis, two cases of worsened dysarthria, two cases of worsened locomotion, one case of hydrocephalus requiring shunting, and one case of need for permanent tracheotomy. In 27 cases of typical and atypical DMD, there were two instances of hemiparesis, two of significant speech deterioration, three of hand ataxia, one of postoperative seizures, and one of hydrocephalus requiring shunting for an overall significant morbidity rate of 21%. The limiting factor in treating secondary dystonia is the underlying spastic paralysis but that in DMD is the relentless postoperative progression. The overall results of this study are remarkably similar to those of other published series: a quarter of the patients improved by 25% to 50%, a quarter to a third by more than 50%. The analysis of effect on specific features of the disease may be useful in the future for predicting outcome in a particular patient.