• From 1986 to 1989, 26 consecutive pediatric liver transplant recipients were followed up at The Hospital for Sick Children, Toronto, Canada. The patients were reviewed to assess the incidence of infection with cytomegalovirus, the severity of disease, and the relationship of recipient and donor serostatus to cytomegalovirus disease. Overall, the incidence of infection was 54% (14/26). Over 90% of patients who were seropositive or whose donors were seropositive developed evidence of cytomegalovirus infection after transplantation. Forty-three percent (6/14) of those with cytomegalovirus infections developed severe, fatal cytomegalovirus disease, despite treatment with immunoglobulins and ganciclovir (Syntex Laboratories Inc, Palo Alto, Calif) or foscarnet sodium (Astra, Pharmaceutical Products Inc, Westborough, Mass). Of all posttransplant deaths, two thirds were associated with severe cytomegalovirus infection. Cytomegalovirus-related deaths occurred in three of four seronegative patients with seropositive donors and three of six seropositive patients with seropositive donors. Therefore, a seropositive donor appeared to be a major risk factor for severe cytomegalovirus disease.