Late-onset sepsis in a preterm twin may harbinger life-threatening sepsis for the asymptomatic co-twin.

We report extremely preterm twins who developed late-onset Escherichia coli sepsis in the second postnatal week within a short time of each other. The asymptomatic twin was not treated initially, and within 2 days developed life-threatening septicemia and meningitis, followed by other serious morbidity. Occurrence of late-onset sepsis in a twin should prompt concurrent investigation and consideration of presumptive treatment of the apparently asymptomatic co-twin.