From 1977 to 1984, 114 eligible patients with invasive squamous cell carcinoma of the vulva and positive groin nodes after radical vulvectomy and bilateral groin lymphadenectomy were randomized to receive either radiation therapy or pelvic node resection. Fifty-three of the 59 patients randomized to radiation therapy received a 4500- to 5000-rad tumor dose in five to 6.5 weeks bilaterally to the groins and to the midplane of the pelvis even if only unilateral positive groin nodes had been detected; no radiation was given to the central vulvar area. Fifty-three of the 55 patients randomized to further surgery had pelvic node resection performed on the side containing positive groin nodes either unilaterally or bilaterally. Acute and chronic morbidity was similar for both regimens. The two major poor prognostic factors were clinically suspicious or fixed ulcerated groin nodes and two or more positive groin nodes. The difference in survival for the 114 evaluable patients was significant, favoring the adjunctive radiation therapy group (P = .03). The estimated two-year survival rates were 68% for the radiation therapy group and 54% for pelvic node resection group. The most dramatic survival advantage for radiation therapy was in patients who had either of the two major poor prognostic factors present; at this time, the benefit of radiation therapy for the remaining patients is uncertain. In this randomized prospective study, the addition of adjunctive groin and pelvic irradiation therapy after radical vulvectomy and inguinal lymphadenectomy proved superior to pelvic node resection.