Rationale: Human Metapneumovirus is a newly described virus isolated in 2001 from children with acute respiratory infection. It has subsequently been reported globally although there is limited data in lung transplant recipients. Objectives: 1) To prospectively analyse whether human Metapneumovirus was circulating in our adult lung transplant community and assess the morbidity of this infection 2) Compare to respiratory syncytial virus, the clinical presentation and outcome following intravenous ribavirin. Methods: Lung transplant patients with clinical features of respiratory viral infection underwent nasopharyngeal aspirates. Patients with a positive specimen for either respiratory syncytial virus or human Metapneumovirus by reverse transcriptase PCR analysis and graft dysfunction received intravenous ribavirin and pulse steroid therapy. Main Results: Eighty-nine patients had 199 visits for aspirate studies. A viral cause was determined for 62 visits in 47 patients (19 human Metapneumovirus, 18 respiratory syncytial virus, 13 parainfluenza, 9 influenza A, 2 adenovirus and 1 influenza B). A significant percentage of Metapneumovirus (63%) and respiratory syncytial virus (72%) patients developed graft dysfunction with average decline in FEV₁ of 30±12.4% and 25.9±11.2% respectively. In these patients, bronchiolitis obliterans syndrome onset or progression occurred in no patients with human Metapneumovirus compared with 5 of 13 (38%) respiratory syncytial virus patients at 6 months. Conclusions: Human Metapneumovirus is a leading cause of acute respiratory tract illness in lung transplant recipients. The incidence and clinical spectrum at presentation are similar to respiratory syncytial virus although the latter does appear to be associated with a higher risk of chronic rejection. We recommend testing for human Metapneumovirus to assess local epidemiological patterns.