The horizontal sacrum has never been described as an indicator of a tethered spinal cord following myelomeningocele closure. We retrospectively analyzed 30 children with a myelomeningocele for this progressive change and its correlation with symptoms. At least two lateral radiographs over time were examined and the lumbosacral angle (LSA) was measured. We found that the majority of these children had an LSA that was greater than would be expected in patients with late and decreased ambulatory abilities. Also, we observed that the LSA was often inappropriately increased at the time many of these patients presented with symptoms indicative of a tethered spinal cord. We hypothesize that the LSA in this group of children is altered by a tethered spinal cord and that the horizontal nature of the sacrum may predate the clinically appreciable symptoms of a tethered spinal cord.