The aim of this study was to establish normal ultrasound measurements of lumbosacral spine in children as a screening assessment of tethered cord or postoperative retethering of cord. Sonography of lumbosacral spine was performed in 108 neurologically normal children (mean age = 2.1 years) using 5- to 12-MHz linear transducer. M-mode was applied at the posterior and anterior subarachnoid spaces just below the conus medullaris and at the L(5)/S(1) dural sac to document cerebrospinal fluid pulsation of the cauda equina. The oscillation rate and amplitude were measured. Sixteen children with spinal cord anomalies (6 with low tethered cord and 10 postoperative cases of low tethered cord) were also examined. The mean posterior/anterior subarachnoid spaces of normal children were 2.6 mm/1.8 mm at the terminal dural sac. The mean oscillation amplitude and rate of the cauda equina were 0.52 mm and 121/min at the L(5)/S(1) dural sac. The oscillation amplitude at this level demonstrated a statistically significant difference between normal and abnormal groups. In conclusion, we recommend taking the fifth percentile of the normal oscillation amplitude at the L(5)/S(1) dural sac as a reference. Any oscillation amplitude of less than 0.3 mm in a symptomatic patient should alert the clinician to possible cord abnormality, cord tethering, or retethering in postoperative cases.