Portal vein gas embolism was demonstrated by ultrasound in a preterm infant with necrotizing enterocolitis. This sign could not be detected radiographically. It is speculated that portal venous gas occurs more frequently than hitherto inferred from radiological studies. This observation points to the value of ultrasonography in providing early objective evidence in support of the diagnosis of NEC. The favourable outcome for the patient proves that portal venous gas embolism is not necessarily associated with a fulminant course of enterocolitis.