In December 2007, inspections conducted by two local health authorities (DDASS) at five medical imaging centers raised concerns about hygiene issues related to the use of endocavitary ultrasound probes (endorectal or endovaginal). The French Institute for Public Health Surveillance (InVS) was then asked to assess the risk of infection associated with these practices. The infection risk associated with endocavitary ultrasounds performed without a biopsy, in the absence of probe protection or disinfection, is unknown. No cases of infection related to this context have been reported in the literature. A systematic analysis of this risk was therefore conducted by a multidisciplinary expert group coordinated by the InVS. The objective of this analysis was to identify a list of infectious agents to be prioritized in order to inform patients exposed to these procedures, offer them screening, and, if necessary, provide treatment. The microorganisms studied are those that, if transmitted, cause acute and chronic infections, which are sometimes asymptomatic. Complications from these infections can be severe—for the patient or the newborn in the case of pregnant women—and are treatable. Based on a review of the available information for each microorganism, the expert group considers the individual risk of contracting an infection following ultrasound procedures to be extremely low. However, given the size of the exposed population and under the worst-case scenario that all ultrasound procedures at the imaging center were performed without protection or disinfection of the probes, the possibility that at least one infection may have occurred following these procedures must be considered. The decision to inform patients and offer them screening must be made after evaluating the benefits and risks, taking into account the potential infection risks during these procedures—which are extremely low on an individual basis—and other factors not considered in this expert assessment (the law of March 4, 2002, stress and anxiety experienced by patients, etc.). If this decision is made, the screening offer should cover five types of infection, in descending order of infectious risk: hepatitis B (in unvaccinated individuals or, if vaccinated, those for whom verification of immunity is unsatisfactory), Chlamydia trachomatis infection, HIV infection, hepatitis C, and syphilis. For women currently pregnant, screening for HIV infection, HBV infection, and syphilis should be offered, if possible, before delivery. However, the existence of well-established and systematic care for pregnant women makes it possible to eliminate risks associated with herpes and Group B streptococcus. Given their prevalence in the general population and their usual modes of transmission, the potential detection of one of these infections does not in any way confirm that it is linked to the ultrasound procedure performed. If a decision is made to inform patients and offer screening, an evaluation of this program must be discussed in order to provide a description of its implementation within the target population. (R.A.)