Varicella-zoster virus (VZV) usually causes localized zoster in adults. However, in immunocompromised patients, it can cause systemic infection accompanied by complications such as pneumonia, encephalitis, and hepatitis. Although most of critically ill patients in intensive care unit (ICU) are immunologically compromised, they are usually not considered to be at risk for systemic VZV infection.We report two cases of systemic VZV infection occurring in critically ill patients in an ICU. One patient was a 69-year-old man with Streptococcus pneumoniae-induced purpurafulminans, and the other was a 75-year-old woman with severe acute pancreatitis. During the clinical course in the ICU, characteristic vesicles with umbilical fossa appeared diffusely and bilaterally on their face, trunk, and extremities. VZV-specific IgG levels were confirmed to be elevated compared to that of the pre-onset, and a diagnosis of recurrent VZV infection was made in both patients. The patients were treated at the same ICU but did not coincide with each other; therefore a cross-infection was unlikely. They were treated with intravenous acyclovir, but the latter patient eventually died of respiratory failure.VZV infection can cause a number of serious complications, and can lead to death in some patients. Early detection and proper treatment are needed to prevent the infection from spreading out and save the patients. It might be necessary to consider antiviral prophylaxis against VZV infection for a part of critically ill patients in ICU, although the effectiveness of this approach is yet to be established.