The use of ultrasound contrast agents has increased over recent years. The Contrast Media Safety Committee (CMSC) of the European Society of Urogenital Radiology (ESUR) decided to review the safety of ultrasound contrast agents in humans and to draw up guidelines. A comprehensive literature search and review was carried out. The resulting report was discussed by the CMSC of ESUR and at the 11th European Symposium on Urogenital Radiology in Santiago de Compostela, Spain, in 2004. Ultrasound contrast agents approved for clinical use are well tolerated, and serious adverse reactions are rarely observed. Adverse events are usually minor (e.g. headache, nausea, altered taste, sensation of heat) and self-resolving. These symptoms may not be related to the ultrasound contrast materials as they have also been observed in placebo-control groups. Intolerance to some components may occur. Generalized allergy-like reactions occur rarely. Ultrasound contrast agents are generally safe. The ultrasound scanning time and the acoustic output should be kept to the lowest level consistent with obtaining diagnostic information. Adverse reactions should be treated symptomatically.