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Objective: To determine the viral aetiology of respiratory infections in children presenting to primary care with ‘‘more than a simple cold’’. Design: Observational study in 18 Oxfordshire general practices over four winters (2000–01 to 2003–04). Patients: 425 children aged 6 months to 12 years with cough and fever for whom general practitioners considered prescribing an antibiotic. Methods: Nasopharyngeal aspirate obtained from 408 (96%) children was subjected to PCR for respiratory viruses. Parents completed an illness diary for the duration of illness. Results: A viral cause of infection was detected in most (77%) children. Clinical symptoms correctly identified the infecting virus in 45 % of cases. The duration of illness was short and the time course was very similar for all infecting viruses. One third of children were prescribed an antibiotic (34%), but this made no difference to the rate of parent-assessed recovery (Kruskal-Wallis, p = 0.67). About one in five children with influenza who did not receive an antibiotic had persistent fever on day 7 compared to no children receiving antibiotics (p = 0.02); this difference remained after adjustment for severity and other factors and was not seen with other viruses. Conclusions: Most children receiving antibiotics for respiratory symptoms in general practice have a