Introduction: Vascular access is a fundamental component of caring for critically ill children and adults. Although a straightforward procedure, establishing vascular access can be very difficult and time consuming, especially in the sickest patients, who at the same time need it the most. Our objective during this pilot study was to evaluate whether infrared imaging can facilitate the localization of vascular structures. Methods: Imaging was performed using a Lockheed Martin LTC-500 uncooled IR camera containing a 320×240 element microbolometer with elements spaced on 46 micron centers. Spectral sensitivity was 8 to 14 micron; thermal sensitivity was 0.02 °C per gray scale level over the physiological temperature range. The camera was equipped with a 50 mm f/.8 lens. The camera was interfaced though a digital output port to a Matrox frame grabber. Infrared images were displayed in real time (60 Hz refresh rate) on a computer monitor. Results: We were able to visualize venous vascular structures in pediatric and adult subjects which were not visible with the naked eye. Images obtained had clinically adequate resolution and were rapidly processed providing live images of arm, neck and scalp veins. Warming of the extremities with a warm water bath resulted in enhancement of vascular images due to greater temperature contrast produced by conduction of the heat along the path of the vessel. Conclusions: This pilot study was used to specify performance characteristics of an application-specific infrared imaging product to be developed in the near future. Infrared technology is likely to facilitate vascular access in critically ill patients by allowing visualization of veins that otherwise cannot be located. This application may reduce the time needed to obtain vascular access and potentially the risk for needle sticks. Patients with difficult access would benefit the most from this technology. The promising results of this pilot study have prompted a prospective randomized study to evaluate the efficacy of this technology while obtaining venous access in critically ill children in our PICU. Future directions include the study of arterial and deep venous vascular applications.