After documentation of a case of life threatening Helicobacter pylori (H. pylori) gastric ulcer in an adolescent girl on treatment for acute lymphoblastic leukaemia, we started to systematically look for gastro-intestinal symptoms due to H. pylori infection in our cancer patients at G. Gaslini Children's Hospital. During a period of 46 months, we observed 13 further cases of severe dyspepsia syndrome or gastro intestinal bleeding associated with presence of H. pylori faecal antigen. All patients recovered with appropriate therapy. H. pylori may represent a cause of severe gastrointestinal complications in children with cancer or following bone marrow transplant.