Prognostic impact of peripheral blood white blood cell count (WBC) at the diagnosis of childhood acute lymphoblastic leukaemia (ALL) was evaluated in a population-based consecutive series of 2666 children aged 1-15 treated for ALL between 1992 and 2008 in the five Nordic countries (Denmark, Finland, Iceland, Norway and Sweden). Ten-year event-free (pEFS(10 y)) survival and overall (pOS(10 y)) survival were 0.75 ± 0.01 and 0.85 ± 0.01, respectively. Although treatment intensity was determined by WBC, non-remission and relapsed patients still had significantly higher WBC than those in remission for B-cell precursor (BCP) (median WBC: 24.8 vs. 14.0 vs. 8.3 × 10(9) /L, P <0.001), but not for T-lineage (T-ALL) (median WBC: 127.8 vs. 113.0 vs. 86.8 × 10(9) /L, P = 0.22). pEFS was inversely related to WBC for BCP (P <0.001), but not for T-ALL. WBC was not associated with risk of event for BCP or T-ALL for patients with minimal residual disease at the end of induction (MRD(d29) )