The frequency of occult developmental defects of the spine is probably
underestimated but could be determined by studies involving routine m
agnetic resonance imaging. Skin abnormalities in the lumbosacral area
are a valuable clue to the diagnosis. A case in a patient with a faun
tail nevus is reported. Neurosurgical treatment should be done early t
o prevent progressive neurologic loss and orthopedic abnormalities.