Human metapneumovirus (hMPV) is a recently described paramyxovirus associated with upper and lower respiratory-tract infection (URI and LRI, respectively). We conducted a prospective study of URI and LRI in adults with hematologic malignancies during a 4-year period. We retrospectively tested samples by reverse-transcription polymerase chain reaction for hMPV and analyzed clinical data. Twenty-two (9%) of 251 episodes of respiratory infection tested positive for hMPV. Sixteen (73%) of the illnesses occurred in hematopoietic stem-cell transplant recipients. Nine patients with hMPV developed LRI; 3 of these patients died. hMPV is a common cause of respiratory infections in adults with hematologic malignancies, with associated morbidity and mortality.