Background. Arterial cannulation is a common anaesthetic procedure that can be challenging and time-consuming in small children. By visualizing the position of the radial artery, near-infrared vascular imaging systems (NIRVISs) might be of assistance in arterial cannulation. The present study evaluates the effectiveness of an NIRVIS in arterial cannulation in infants. Methods. An observational study was conducted in patients up to 3 yr old, undergoing arterial cannulation before cardiothoracic surgery. Arterial cannulation was performed as usual in 38 patients, and subsequently with the NIRVIS in 39 patients. Results. The time to successful cannulation was 547 s (171-1183) without and 464 s (174-996) with the NIRVIS (P=0.76) and the time to first flashback of blood was 171 s (96-522) and 219 s (59-447), respectively (P=0.38). There was a tendency in favour of the NIRVIS in success at first attempt: 12/38 and 7/39, respectively (P=0.29) and in the number of punctures: 6 (2-12) and 3 (1-7), respectively (P=0.10). Conclusions. The present study did not show a significant clinical improvement when NIR light was used during arterial cannulation in small children. There is a large difference between time to first flashback of blood and time to successful cannulation, indicating that inserting the cannula, and not localizing the artery, is the main difficulty in arterial cannulation in children. © 2012 The Author. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved.