Human metapneumovirus (hMPV) was first identified in 2001 in Dutch children with bronchiolitis. The virus is an RNA virus in the Pneumovirinae subfamily and is most closely related to respiratory syncytial virus. hMPV has been shown to have worldwide circulation with nearly universal infection by age 5. Similar to influenza and respiratory syncytial virus, activity is greatest during the winter in temperate climates. Most of the available data on the clinical manifestations of hMPV infection are from studies of children where the virus causes upper respiratory tract infections, bronchiolitis, and pneumonia. Reinfections with hMPV occur throughout adult life and hMPV infection has been documented in 1-9% of adults each year using RT-PCR and serology for diagnosis. Illness is generally mild in young adults with serologic evidence of asymptomatic infection in many cases. Adults at highest risk of serious sequelae as a result of hMPV include the elderly, adults with underlying pulmonary disease, and those who are immunocompromised. Outbreaks of hMPV have been documented in long term care facilities with mortality of up to 50% in frail elderly residents. In addition, 6-12% of exacerbations of chronic obstructive pulmonary disease have been associated with hMPV and underlying lung disease is common in patients hospitalized with hMPV. Lastly, hMPV has been linked with severe idiopathic pneumonia in recipients of hematopoietic stem cell transplants. Although the true spectrum of adult hMPV remains to be defined, it is clear that hMPV can result in severe illness the frail elderly and adults with underlying diseases.