We report a case of a 34-month-old girl who presented with acute atraumatic intermittent limp. History and examination at this stage were not suggestive of an underlying serious disorder, but routine blood testing revealed abnormal results and prompted further investigations. She was subsequently diagnosed with acute lymphoblastic leukaemia. This case illustrates how routine phlebotomy lead to early diagnosis and facilitated instant therapy resulting in a significantly improved outcome for the child.