Real-time ultrasonography (US) is frequently used to access the biliary tree, urinary system, and pleural cavity, as well as abscesses and other fluid collections, but is rarely used to access blood vessels. This article describes the clinically indicated circumstances and technical aspects of US-guided access to veins and arteries. The authors' experience suggests that appropriate use of this modality significantly simplifies vascular access difficulties, reduces procedure time and morbidity, and is cost-effective.