It has increasingly come to be recognized that critically ill patients who are traditionally considered immunocompetent may also be at risk for CMV infection. For example, septic insult as a result of bacterial or fungal infections has the potential to promote the release of immunomodulatory cytokines and lead to reactivation of CMV [6, 7] . Reactivation from the latency rather than primary infection is believed to be the cause of CMV infection because none of the critically ill CMV seronegative patients developed CMV infection as opposed to 13 to 56% of seropositive patients [8, 9] . Several observational studies have shown an association between CMV infection in critically ill patients and poor clinical outcomes [8, 10, 11] . However, available data are limited by relatively small sample sizes, diversity in patient populations studied, difference in methodological assays employed for CMV, and variability in reported outcomes that preclude generalizability of the results of the individual reports. The objectives of this review are to summarize the frequency and predictors of CMV infection, and outcomes in critically ill immunocompetent patients with CMV infection. Additionally, we discuss the pathophysiologic basis of CMV reactivation and the implications of these data for optimizing outcomes in critically ill patients.