Between 1973 and 1977, 48 patients less than 65 years old with non-Hodgkin's malignant lymphoma (NHML) of poor prognosis (+/- high grade malignancy, +/- clinical stages III or IV, +/- first or repeated relapse) were included in a prospective clinical trial. After complete remission (CR), obtained with chemotherapy and radiotherapy, patients were randomized to receive bacillus Calmette-Guérin (BCG) or no further therapy. BCG was administered in weekly scarifications up to 3 years. Forty-three patients are assessable. Twenty-four patients have relapsed: nine out of 21 in the BCG group, and 15 out of 22 in the control group. There is a significant difference in favor of the BCG group in disease-free survival (P = .03). Twenty-one patients have died, 18 from NHML: seven in the BCG group, and 11 in the control group. There is a significant difference in favor of the BCG group for overall survival at 10 years (P = .05). A multivariate analysis points out BCG as a significant prognostic factor. Adjuvant BCG may improve particularly disease-free survival and overall survival for patients with clinical stages I and II or intermediate- and high-grade malignancy. These results suggest that in patients less than 65 years old with NHML of poor prognosis, BCG may significantly increase disease-free survival and overall survival.