A 2-month-old male infant presented to hospital for the third time in late autumn with a 4 week history of cough and respiratory distress. He had presented to hospital on two occasions during the previous two weeks, and had twice been discharged with a diagnosis of bronchiolitis, based on clinical findings and the season. That the nasopharyngeal aspirate (NPA) was negative for respiratory viruses did not alter the diagnosis as this was felt to be a common false negative finding. However his cough worsened and on his third presentation he had respiratory distress with bilateral crackles and wheeze. The C reactive protein was 121 mg/l but the NPA was again negative for viruses. He was investigated for atypical causes of lower respiratory tract infection and the NPA was positive for Chlamydia trachomatis by polymerase chain reaction. He was treated with a 5 day course of azithromycin and made a full recovery.