In 5 children with acute lymphoblastic leukaemia (ALL) splenomegaly occurred or persisted after induction of haematological remission. 3 patients underwent splenectomy but the spleen was free of leukaemia in each case; these patients relapsed and died 10 to 28 months after surgery. 2 patients who were not splenectomised are alive and free of leukaemia 2 and 6 years after splenomegaly was first noted; in 1 splenomegaly regressed after cessation of antileukaemic therapy. The isolated finding of splenomegaly in children with ALL in haematological remission does not necessarily indicate a relapse; instead, it is suggested that splenic enlargement may reflect an immunological process contributing to control the leukaemia and that removal of the spleen may be harmful.