In 2005, a new human coronavirus, HCoV-HKU1, was identified in Hong Kong. We screened respiratory specimens collected from December 16, 2001, to December 15, 2002, from children <5 years of age who tested negative for respiratory syncytial virus, parainfluenza viruses, influenza virus, and adenovirus for HCoV-HKU1 by reverse transcription-polymerase chain reaction. Overall, 1,048 respiratory specimens from 851 children were tested, and 9 HCoV-HKU1-positive children (1%) were identified, 2 of whom had 2 positive specimens. Children who had HCoV-HKU1 infection had evidence of either upper or lower respiratory tract infection or both. Two patients had disease beyond the respiratory tract. HCoV-HKU1 was identified from December 2001 to February 2002. Sequence analyses suggest that a single strain was circulating. HCoV-HKU1 is therefore likely circulating in the United States and is associated with upper and lower respiratory tract disease.