A young child was admitted with a cauda equina syndrome believed to be
progressive, but unrelated to a congenital anomaly, Magnetic resonanc
e imaging studies revealed the presence of an intradural tumor in the
cauda equina, A yellow pasty tumor with nerve root infiltration was id
entified at surgery. Histologic features were pathognomonic for histio
cytosis X. The patient's management and review of the literature are d
iscussed.