The United Kingdom Childhood Cancer Study (UKCCS) was specifically designed to investigate the potential etiological role of infections as one of its objectives and information on a number of markers of infectious exposure from multiple sources was collected (www.ukccs.org). This study found that a mother's recollections of past minor illness episodes in her children were unreliable, producing systematic case-control differences. From birth onwards children diagnosed with ALL between 2-5 years were found to have had more clinically diagnosed infectious illness episodes (not fewer) than unaffected children, with those with two or more neonatal infections being diagnosed with leukaemia around 7 months earlier than those with only one or none. The findings from these analyses and their implications for future research are reviewed and discussed in this paper.