OBJECTIVE To study the clinical features and treatment of severe pneumonia due to novel influenza A (H1N1) virus in children with lymphoma during chemotherapy. METHODS The clinical manifestations, radiologic features, reasons of misdiagnosis, experiences in treatment and prognosis of 4 children with lymphoma complicated with pneumonia due to novel influenza A (H1N1) virus during chemotherapy were analyzed retrospectively. RESULTS Four children out of the 54 patients with hematologic disorders who were receiving chemotherapy suffered from H1N1 influenza. Neutrophil counts were less than 0.5 × 10(9)/L in all 4 patients. The body temperature was higher than 39°C accompanied by chill and low blood pressure at the onset of the illness. Dyspnea and hypoxemia occurred quickly. Two of them developed acute respiratory distress syndrome (ARDS). C-reactive protein (CRP) was higher than 50 mg/L in all these cases, and was higher than 200 mg/L in 2 cases. Chest X-ray showed that there were extensive infiltrations in several lung lobes in all the 4 patients. The first patient was misdiagnosed as sepsis at the beginning. The results of 17 blood cultures for the 4 patients were all negative. Fungi were found in 2 of 20 sputum cultures in 2 patients and these 2 patients had been considered as having fungal pneumonias. All the 4 patients were treated with oseltamivir phosphate. The oseltamivir treatment started on the 5(th) day in patient number 1, whereas on the 1(st) day in the other 3 patients. Intravenous immunoglobulin (IVIG) was used in all 4 patients. Methylprednisolone was used in 3 patients. After treatment, 2 died and 2 were improved. CONCLUSIONS The children with lymphoma who undergo chemotherapy are prone to develop severe pneumonia during epidemics of influenza A H1N1. The pneumonia may be aggravated very quickly and have a higher mortality. The patients might be easily misdiagnosed as sepsis at early stage. The pneumonia may be misdiagnosed as fungal infection. During H1N1 prevalent season when high fever occurred, H1N1 infection should be considered. Early detection of the virus and use of oseltamivir phosphate and high-dose IVIG and methylprednisolone might reduce the mortality.