A sacral dimple is an indentation, present at birth, in the skin on the lower back. It's usually located just above the crease between the buttocks. Most sacral dimples are harmless and don't require any treatment.
Sacral dimples that are accompanied by a nearby tuft of hair, skin tag or certain types of skin discoloration are sometimes associated with a serious underlying abnormality of the spine or spinal cord. In these instances, your child's doctor may recommend an imaging test. If an abnormality is discovered, treatment depends on the underlying cause.