It has been reported that cytomegalovirus (CMV) infections increase the susceptibility of transplant patients for other opportunistic infections. Most of these studies date back from a time when CMV infection was difficult to diagnose and antiviral treatment not available. We therefore analyzed CMV-related morbidity after OLT in 111 consecutive patients. CMV monitoring was done weekly using the antigenemia assay, a quantitative marker of the viral load, in addition to serology. CMV infection occurred in 66/95 (69%) evaluable patients. Antigenemia was detected in 94% of them. The number of CMV antigen-positive cells was helpful to monitor the course of infection and differentiate CMV disease from other complications. CMV infection was symptomatic in 48/66 (73%) patients. Mild disease occurred in 30 patients, and severe constitutional symptoms or organ involvement in 18. No patient died as a direct result of CMV infection, but mortality between day 30 and 180 tended to be higher in CMV-infected patients (15 vs. 0%, p < 0.1). CMV infection was associated with a 2.45-fold higher incidence of major infections between day 30 and 180 after OLT (p < 0.05). Most of these infections were caused by gram-positive cocci. We conclude that CMV not only causes substantial morbidity, but also increases the risk of bacterial infections.