We have experienced and treated seven patients of pre-B cell leukemia in childhood. Clinical, cytological and ultrastructural characteristics of them were studied. Most of them had higher counts of white blood cells, hepatosplenomegaly, high value of lactic dehydrogenase and various karyotype abnormalities at onset. The chromosomal translocation t (1; 19) that is supposed to be specific to pre-B cell ALL was found in four of seven of our cases. In the seven patients, survival was studied in comparison to that of 27 common ALL patients at our hospital that are common in childhood acute leukemia. Although no difference in remission duration and survival time between pre-B cell ALL patients and common ALL group, there have been seen the tendency that remission and survival were of shorter duration for patients with pre-B cell ALL.