From September, 1967, to January, 1974, a clinical trial was carried out by the WHO Melanoma Group to evaluate the efficacy of elective lymph-node dissection in the treatment of malignant melanoma of the extremities with clinically uninvolved regional lymph nodes. Treatment was prospectively randomized: 267 patients to excision of primary melanoma and immediate regional-lymph-node dissection and 286 to excision of primary melanoma and regional-lymph-node dissection at the time of appearance of metastases. The statistical analysis showed no difference in survival between the two groups of patients, regardless of how the data were analyzed (according to sex, site of origin, maximum diameter of primary tumor or Clark's level or Breslow's thickness). Elective lymph-node dissection in malignant malanoma of the limbs does not improve the prognosis and is not recommended when patients can be followed at intervals of three months.