Pandemic influenza A (2009-H1N1) usually results in mild clinical illness, but in some individuals it can be life-threatening. There are no reports of this disease among paediatric patients with acute lymphoblastic leukaemia (ALL). We report ten consecutive patients with ALL and pandemic influenza treated in a single institution. Median age was 7 years (range: 3–12). All were treated with oseltamivir. There were no deaths. Two patients under intensive chemotherapy developed pneumonia and one required ventilatory support. ALL patients under maintenance treatment had mild disease. In conclusion, in our series only patients under intensive treatment developed a moderate to severe disease.