Risk directed treatment forms a central component of modern protocols for childhood acute lymphoblastic leukaemia (ALL). A review of recent studies of minimal residual disease (MRD) analysis shows that it is a powerful prognostic factor in both first line and relapse treatment. However, the value of MRD analysis is both time point and protocol specific, and the threshold for MRD detection of the technique used impacts upon the results obtained. MRD analysis does have a useful role to play in the risk directed treatment of childhood ALL, and this is currently being investigated in large prospective studies.