A vertebral attachment system and method for retaining a spinal vertebra (25) on a rod (2) employ a device (1) including a body (3) for attachment to the rod, a flexible strip (4) for linking the vertebra to the attachment body and a means (5) for adjustably locking the flexible strip on the attachment body. The attachment body (3) is made of a single part having a U-shaped cross-section, for passing the rod between the bottom wall (10) of the U and the adjustable locking means. The adjustable locking means (5) consists of a linking part (18) connecting the opposite ends of the two arms (6, 7) of the U, arranged such as to compress the rod against the wall. The arms (6, 7) each include a recess (14) opposite thereof, located on the bottom side of the U, for passing the two ends of the strip between the bottom and the rod in order to form a loop for attachment to a vertebra.