The case histories of 293 adolescent and adult patients with acute lymphoblastic leukemia (ALL) first seen and treated between 1969 and 1979 are reviewed. A complete remission (CR) was achieved in 79% of cases. Male sex, advanced age (greater than or equal to 30 yr old), and early CNS involvement were the major determinants of remission failure. Median duration of first CR was 16 mo, with 23 patients (actuarial proportion 25%) alive and relapse-free at 5 yr. The major determinant of first CR length was white blood cell (WBC) count (best cut-off value at 35 X 10(9)/liter). First CR length was also negatively affected by early CNS involvement, morphological FAB L3 subtype, and B-cell (Smlg+) leukemia, but these features were significantly associated with a high WBC count. First CR length in patients 11–15 yr old did not differ significantly from that of patients 16–59 yr old. The negative prognostic value of T-cell (E+) leukemia was not confirmed in this adult series. CNS prophylaxis provided an effective protection against CNS relapse. Maintenance chemotherapy was apparently more effective when 4 or more than 4 drugs were employed. “Low risk” patients (WBC count less than 35 X 10(9)/liter still relapsed rather frequently (32% at 1 yr, 49% at 2 yr), with 33% of them alive and relapse-free at 5 yr. “High risk” patients (WBC count greater than or equal to 35 X 10(9)/liter +/- early CNS involvement +/- morphological L3 subtype +/- B-cell leukemia) relapsed very quickly (50% at 6 mo. 70% at 1 yr), with only 6% of them relapse-free at 5 yr.