There is a dearth of information on the mortality of children with cancer in Nigeria but the few available reports suggest a poor outcome. The objectives of this study were to determine the underlying and immediate causes of death from childhood cancer. The mortality summary cards of all cases of childhood cancer seen at the Department of Paediatrics, University College Hospital, Ibadan between January 1998 and December 2004 were reviewed. Eighty-eight cases of childhood cancer were seen, out of whom 52 (59.1%) died, but only the 48 deaths with complete data were analyzed. These deaths comprised of 37 males and 11 females giving a male:female ratio of 3.4:1. Their ages ranged from 1 to 13 years with a mean of 7.3 +/- 3.4 years. The majority (71.4%) of all patients presented with diffuse or metastatic disease at diagnosis and this was associated with increased risk of dying. Of the 48 cases reviewed, 39 (81.3%) died without any remission of the primary tumour including 5 (10.4%) with disease progression despite treatment and 15 (31.3%) who died before treatment; only 4 cases (8.3%) died from tumour relapse. The immediate causes of death were infections (39.6%), bone marrow suppression (29.2%), treatment-related mortality (27.1%), organ failure (22.9%), bleeding (16.7%) and other metabolic causes (8.3%). Potentially reversible factors such as infections, bone marrow suppression and treatment-related events are the commonest causes of death from childhood cancer in Ibadan. Therefore, early presentation, prompt identification and effective management of these problems may reduce childhood cancer mortality in Nigeria.