In order to appreciate their prognostic value in acute lymphoblastic leukemia (ALL) of childhood, the main initial clinical and biological features have been analysed in 63 patients. In all cases, follow-up was longer than 3 years; in 43 it was longer than 5 years. The survival rate in first remission was 52% after 3 years and 30% after 5 years. No relapse was observed after 5 years. In this series, the presence of very high leukocyte count (less than 30 x 10 9/l or 30,000/mm3) and sex were the only significant prognostic factors. A poorer prognosis of ALL was indeed present in boys. The sex-related difference is independent from other prognostic factors and may require special attention.