Seven cases of infant acute lymphoblastic leukaemia with t(11; 19) (q23; p13) are described. They are characterized by a high white cell count, organomegaly, early central nervous system (CNS) disease, and a poor prognosis. Blasts are usually of an immature early B-cell lineage although monocytoid features are present in some cases. The characteristics of infant acute leukaemia with t(11; 19) are very similar to those found with t(4; 11), and the presence of t(11; 19) may indicate the same poor prognosis.