The length of hospital stay (LOS) for patients with respiratory virus infections has been reported to depend the virus type and infection severity. However, the impact of co-infections remains unclear. Patients with suspected respiratory virus infections, who visited Dankook University Hospital between December 2006 and February 2014, were included to examine the relationship between co-infections and LOS. Multiplex reverse transcriptase-polymerase chain reactions were used to identify the causative viruses. LOS was analyzed with respect to sex, age, virus, and co-infection. During this period, 5,310 out of the 8,860 patients (59.9%; median age, 1.5 years) were respiratory virus-positive. In respiratory virus-positive patients with single, double, and three-or-more infections, the average LOS was 7.3, 6.7, and 6.6 days, respectively. Longer LOS was observed for older patients and those with human coronavirus OC43 infections compared with adenovirus or respiratory syncytial virus A infections. LOS differed significantly according to age, virus type, and co-infection, but not between double and three or more infections.