A severely ill 2-month-old female infant was admitted with meningitis and septicaemia caused by Streptococcus pneumoniae. The patient, who also had an acute cytomegalovirus (CMV) infection, revealed the typical clinical and biochemical characteristics of type I tyrosinaemia (TIT). Clinical evidence of severe hepatocellular damage was shown, but urinary succinylacetone was not detected. The diagnosis of TIT was finally confirmed by decreased activity of fumarylacetoacetase (FAA) in skin fibroblasts from the patient and both parents. Following dietary treatment and after overcoming the bacterial and viral infection, the patient's liver function improved.