Cytomegalovirus (CMV) infection can occur throughout life. Similar to other herpesviruses, after primary infection CMV remains in the host in a latent state. Infection of the immunocompetent host does not cause clinical symptoms, whereas infection of the immunocompromised host can cause severe and even fatal disease. Morbidity and mortality associated with primary CMV infection or with reactivation from latency is common in immunosuppressed transplant recipients and in patients with immunodeficiency caused by HIV infection. CMV pneumonia is considered the immediate cause of death in these patients.