A totally laboratory-based system for surveillance of hospital-associated infections is not sensitive enough, but may be a base for surveillance of urinary tract infections. The SENIC study has convincingly demonstrated that for the four most important hospital-associated infections in the U.S., active ongoing intense surveillance based on daily patient chart and/or Kardex reviews in itself reduces the infection rate. Studies in other countries indicate that for postoperative wound infections this holds true also outside the U.S. For other types of nosocomial infections, similar studies outside the U.S. are urgently needed. The SENIC study underlines the importance of infection control nurses, but also of well-trained hospital epidemiologists.