Several etiological factors have been suggested in the pathogenesis of extrahepatic biliary atresia (EHBA); congenital, metabolic, infectious, and multifactorial. Herein we present a study of 10 children with EHBA, the aim being to explore viral infection as a possible cause of their condition. During a period of 2 yr, all infants with EHBA were included in a study and examined on viral disease on admittance for Kasai operation. In eight of the 10 children and in one parental couple the laboratory results suggested recent or persistent viral infection. Four infections were caused by cytomegalovirus (CMV) and another five by Epstein-Barr virus (EBV). CMV-DNA was detected in two liver biopsies, EBV-DNA in one liver biopsy. In a control group of 10 patients matched by age and tested by PCR in serum and viral antibodies, no sign of viral infections were detected. CMV or EBV infection were present in an unexpectedly high proportion of infants with EHBA, justifying exhaustive examination on viral disease in these children.