In the months of July and August 2003, an outbreak of acute respiratory illness caused by influenza A virus occurred among students in seven residential schools situated in the northern part (Perak) of Peninsular Malaysia. Out of 4989 students, aged 13 to 18 years (mean = 15.9), 1419 (28%) were effected by influenza-like illness. All patients were treated as outpatients except for 36 students who required admission for high fever, severe coughing and shortness of breath. Abnormal chest X-ray findings were noted for those that required inpatient management. Influenza A virus was isolated from 37 sputum specimens, 20 throat swabs and three nasal swab specimens from a total of 278 clinical samples obtained from 180 patients. Isolates from each of the outbreaks were sent to WHO Collaborating Centre for Reference and Research on Influenza, Melbourne, Australia for antigenic and genetic analysis. One school outbreak was due to influenza A (H1N1), A/New Caledonia/20/99-like virus while the other six school outbreaks were due to influenza A (H3N2) viruses which were A/Fujian/411/2002-like).