Acute lymphoblastic leukaemia (ALL) is seen in both children and adults, but its incidence peaks between ages 2 and 5 years. The causation of ALL is considered to be multi-factorial, including exogenous or endogenous exposures, genetic susceptibility, and chance. The survival rate of paediatric ALL has improved to approximately 90% in recent trials with risk stratification by biologic features of leukaemic cells and response to therapy, therapy modification based on patient pharmacodynamics and pharmacogenomics, and improved supportive care. However, innovative approaches are needed to further improve survival while reducing adverse effects. While most children can be cured, the prognosis of infants and adults with ALL remains poor. Recent genomewide profiling of germline and leukaemic cell DNA has identified novel submicroscopic structural genetic alterations and sequence mutations that contribute to leukaemogenesis, define new ALL subtypes, influence responsiveness to treatment, and may provide novel prognostic markers and therapeutic targets for personalized medicine. Epidemiology ALL, like cancer in general, is likely to arise from interactions between exogenous or endogenous exposures, genetic (inherited) susceptibility, and chance (figure 1). These factors account for the approximately 1 in 2000 risk of childhood (0-15 years) ALL. The challenge is to identify the relevant exposures and inherited genetic variants and to decipher