This study was aimed to observe the incidences and types of hospital infections and to compare the length of hospitalization and of the operation between the infected patients and those of non-infected after the operations. The subject of study were 465 patients who had been operated surgically in a University Hospital from March 1 to April 30, 1985. The data were clected by reviewing medical charts of subjects. The criteria to diagnose hospital infection for this study had been revised the one utilized at University of Virginia Hospital in the U.S. Summary of the results were as follows; 1. The incidence rate of hospital infection was 6 %. The type of infection with higher incidence rate in order were wound infection(28.5%) urinary infection(28.5%), fever of unknown origin (25%) and septicemia (18%). 2. There was a statistically significant difference in the duration of hospitalization between the patient group without it (t=265.2, p<0.005). 3. There was a statistically significant difference in the duration of operation between the patient group with it (t=75.0, p<0.005).