Cytomegalovirus (CMV) infection is the most important congenital viral infection. Intravenous (i.v.) Ganciclovir (GCV) improved outcome in term infants with symptomatic congenital CMV infection. We present data on oral valganciclovir (VGCV) in an extremely low birth weight infant. A male preterm infant was delivered at 28 weeks of gestation because of abnormal fetal perfusion with severe intrauterine growth retardation. The infant developed hepatitis and a severe thrombocytopenia. Serology revealed a positive CMV IgM in maternal serum 3 days after delivery and CMV DNA was detected in plasma and urine samples of the infants. Treatment with i.v. GCV was started at day 4 of life for 35 days and continued with oral VGCV for further 6 weeks. Plasma GCV levels were 1.68 ng ml(-1) (peak) and 0.92 ng ml(-1) (trough) on day 10 of oral treatment. Clinical signs resolved and virus load decreased slowly during therapy. At discharge brain stem-evoked audiometry was normal. Oral treatment with VGCV in an extremely low birth weight preterm infant with congenital CMV infection resulted in adequate GCV plasma levels, reduced effectively the CMV viral load and was well tolerated without apparent adverse effects.