Respiratory viruses were identified by the polymerase chain reaction (PCR) in more than 4,200 specimens collected during 2002 and 2003 in Victoria, Australia from patients admitted to hospitals or participating in an influenza surveillance program. Influenza viruses and picornaviruses were important causes of morbidity in both years. Additional testing of picornavirus-positive samples suggested that rhinoviruses but not enteroviruses were more likely to be associated with respiratory symptoms, irrespective of the season in which they circulated. Detection of influenza viruses was strongly associated with the clinical symptoms of cough, fever, and fatigue; but each of the other respiratory viruses occasionally caused these symptoms or was responsible for symptoms severe enough to require hospitalization. Human coronaviruses HCoV-OC43 and HCoV-229E circulated at low levels throughout the study period with peak activity in winter, but overall did not circulate as widely as has often been reported for these agents. Evidence for the human metapneumovirus (hMPV) was only sought in the second year of the study and revealed low-level circulation of this virus, mainly in the cooler months among the very young and adult populations. The detection rate of all viruses declined with increasing age of the patient, particularly in hospital patients. Infection with more than one respiratory virus occurred in a small number of patients; picornaviruses were most commonly implicated in these dual infections.