The results of surveillance of hospital acquired infection at the Johns Hopkins Hospital for a six-month period are reported. Surveillance by a nurse-epidemiologist which seemed to be the most satisfactory method was used in this study. Incidence of nosocomial infections was approximately 4%. Wound infections developed most frequently in patients undergoing extensive intraabdominal procedures or those involving insertion of foreign bodies. A decline inStaphlococcus aureusinfections since 1965 was documented. Infection with gram-negative bacilli, nosocomial urinary tract infection, and septic phlebitis related to the use of intravenous catheters are attracting increasing attention. The case fatality rate in association with nosocomial infection was 1.7%, and approximately one in 1,500 patients admitted to the hospital died with an infection acquired there. Measures for prevention of many of these infections have been established.