Thirty-six patients with Parkinson's disease and medically refractory tremor underwent stereotactic ventrolateralis thalamotomy at the Mayo Clinic between 1984 and 1989. All patients had been or were being treated with carbidopa/levodopa but with unsatisfactory tremor control. Modern stereotactic techniques, including microelectrode recording, were used to treat 36 patients, of whom 31 (86%) had complete abolition of tremor and three patients (5%) had significant improvement. Tremor recurred in two patients within 3 months of surgery; however, the remaining patients suffered no recurrence of tremor during follow-up periods ranging from 14 to 68 months (mean 33 months). Persistent complications (arm dyspraxia, dysarthria, dysphasia, or abulia) were noted in five patients but were a source of disability in only two. It is concluded that thalamotomy in carefully selected patients is a beneficial operation for the control of medically refractory parkinsonian resting tremor.