Bone demineralization is a common condition in very preterm infants. It can easily be detected on plain chest films which are often taken in these patients for other reasons. On the first day of life each vertebral body is formed by two x-ray dense plates which are separated by a smaller horizontal more radiolucent zone. As a result of a calcium and/or phosphorus deficient nutrition the plates loose their x-ray density. Within four weeks the vertebral bodies appear then as a thin x-ray dense outer border surrounding a radiolucent "empty" center.