Objective: Asthma is common in Australian children, with a prevalence of 30%. Airway inflammation is an important determinant of asthma symptoms. Chemotherapy used for the treatment of many childhood cancers suppresses inflammation. The prevalence of asthma symptoms in children treated with chemotherapy is unknown. Methodology: We therefore performed a survey of symptoms of asthma in children attending the oncology clinic at John Hunter Children's Hospital during the first 6 months of 1996. Results: Fifty children aged 1-17 years were surveyed. Thirty-two of the children were in remission and had completed treatment with chemotherapy and 18 were currently undergoing treatment with chemotherapy. There was no significant difference in the prevalence of asthma in children before, during and after chemotherapy (26%, 22% and 34%), or in the prevalence of asthma in their siblings (28%). No child was classified as having persistent asthma while on chemotherapy and there was a significant reduction in the requirement for preventive asthma drugs 12% versus 0% (P = 0 03) being reported during chemotherapy. Conclusion: The prevalence of asthma in children who develop cancer is similar to their siblings and the same as the population as a whole. While asthma symptoms do not disappear completely during chemotherapy, the seventy of asthma symptoms is less, with no need for asthma preventive treatment. The immunosuppressive side effects of the chemotherapy used in the treatment of childhood cancer appear to induce a remission in asthma symptoms. The ongoing requirement for bronchodilator therapy in patients whilst on chemotherapy suggests airway hyperreactivity persists in children while they are on chemotherapy. Prospective study of the airways of this group of patients promises to provide insights into the relationships between airway hyperreactivity, airway inflammation and asthma.