In Korea, the nosocomial infection control program is not well estabilished. This study was carried out to investigate the incidence rate of nosocomial infection occurred among patients of 18 hospitals for 7 days ; cases of hospital infection per 10,000 patients discharged during the same period in Korea. The study was done in 18 volunteer hospitals and nosocomial infection cases for 7 days were collected retrospectively. The result was as follows; 1. The incidence rate of nosocomial infection for 7 days was 578 cases per 10, 000 patients discharged. 2. Pneumonia was the most prevalent nosocomial infection ; the incidence rate 112.7 cases per 10,000 discharges. The incidence rate of urinary tract infection was 85. 7 cases and that of septicemia was 36. 7 cases per 10, 000 discharges. 3. The incidence rate of nosocomial infection among patients of neurosurgery department was the highest(2,742 cases per 10,000 discharges). And the incidence rate of nosocomial infection was 6 times higher among the patients of intensive care unit than that of general ward. The reasons of higher nosocomial infection rate of intensive care unit and neurosurgery appeared to be due to many invasive procedures. Thus the priority in nosocomial infection control program must be given to those groups.