In Japan, we encountered a pandemic expansion of novel influenza A(H1N1) in September 2009, but the impact on patients with underlying disease remained unclear. The Tokyo Children Cancer Study Group (TCCSG) established a "novel influenza information-sharing system" to share real time information on how the novel influenza affects pediatric patients with cancer or other hematologic disorders. To facilitate reporting, we limited the items to only the basic data (underlying disease, age, sex), influenza-associated data (diagnostic method, therapy and outcome) and allowed space for free comments. We could share the information promptly, and found that this system worked well. One hundred and fifteen patients were reported between September 2009 and February 2010. Although eight patients needed to be hospitalized, none of the patients died, were admitted to intensive care units or demonstrated sequelae. The novel influenza A(H1N1) did not have a strong impact on pediatric patients with cancer or hematologic disorder at least during the 2009-2010 season.