The relationship of a variety of initial features and the outcome of therapy was analyzed for 363 children with acute lymphocytic leukemia (ALL). All had entered "total therapy" studies between 1962 and 1971. The standard for comparing outcome of therapy was whether patients with a given feature attained or exceeded the median duration of complete remission, hematologic remission or survival for the group. The results showed that, in general, the more massive or extensive the disease at diagnosis, the poorer the outcome. Factors associated with a significantly poorer prognosis included: initial leukocyte count above 100,000/mm; spleen enlargement greater than 5 cm; mediastinal involvement and early CNS involvement. Children over 10 years old at diagnosis and Negro children also had a poor prognosis. From another viewpoint features were examined for patients who attained at least 3 years of continuous complete remission. This confirmed some earlier findings and, in addition, showed that children under 2 years of age at diagnosis or with hepatomegaly over 5 cm were less likely to attain this goal. With the exception of early CNS involvement, however, patients with excellent responses to therapy were found with each factor of poor prognosis. Two major factors were not analyzed because their relationship to prognosis is generally accepted: therapeutic differences and acute nonlymphocytic leukemia.