To evaluate the effect of real-time ultrasound guidance using a regular or Doppler ultrasound technique for placement of central venous catheters. We searched for published and unpublished research using MEDLINE, citation review of relevant primary and review articles, conference abstracts, personal files, and contact with expert informants. From a pool of 208 randomized, controlled trials of venous and arterial catheter management, eight published randomized, controlled trials were identified. In duplicate, independently, we abstracted data on the population, intervention, outcome, and methodologic quality. Ultrasound guidance significantly decreases internal jugular and subclavian catheter placement failure (relative risk 0.32; 95% confidence interval 0.18 to 0.55), decreases complications during catheter placement (relative risk 0.22; 95% confidence interval 0.10 to 0.45), and decreases the need for multiple catheter placement attempts (relative risk 0.60; 95% confidence interval 0.45 to 0.79) when compared with the standard landmark placement technique. When used for vessel location and catheter placement real-time, ultrasound guidance or Doppler ultrasound guidance improves success rates and decreases the complications associated with internal jugular and subclavian venous catheter placement.