Between 1980 and 1998, in the north-west of England, a significant rise in childhood acute lymphoblastic leukaemia was caused by an increase in the precursor B-cell form of this disease. We analysed data on children who were diagnosed with leukaemia in Yorkshire, UK, between 1974 and 1997. The incidence of acute lymphoblastic leukaemia remained stable, although a non-significant yearly increase of 2.4% was noted for the precursor B-cell form of this disease from 1980 onwards. The precursor B-cell form accounted for 80% of all acute lymphoblastic leukaemia. Our data are not consistent with increasing incidence for precursor B-cell acute lymphoblastic leukaemia, although numbers of children with acute myeloid leukaemia are rising.