17 patients had thalamotomies for alleviation of pain due to malignancy since January, 1970. In 12 of them, thalamic electrodes were implanted through occipital burr holes for subsequent radiofrequency thalamotomies. In 4 cases, the lesions were made by the bifrontal approach and 1 case was approached from the left occipital and right frontal. In 13 cases, the thalamic lesions were made in the vicinity of pulvinar, ventrocaudalis, parvocellularis, centromedianum and/or the adjacent structures. The size of histologically verified lesions in 7 specimens was 3 × 4 × 47 mm maximum and 4 × 3 × 4 mm minimum. Three of the 17 cases required no analgesics between thalamotomy and death or at least 6 months. In these cases, thalamic lesions were made in the vicinity of the posterior medial portion of thalamic nuclei and in one case the lesion was extended to the anterior thalamic radiation. In 7 cases requiring nonnarcotic analgesics, the lesions were located in the vicinity of the posterior median portion of thalamic nuclei, involving pulvinar, ventrocaudalis posterior, centromedian, internal medullary lamina or medial mass of thalamus. The remaining 8 thalamotomies in 7 patients required narcotics. In 4 of them, the lesions were made outside the posterior medial portion of thalamic nuclei. Histological confirmation is available in 6 cases.