A 24-day-old, 2.2-kg, female Reeves' muntjac (Muntiacus reevesi) acutely developed left hind limb lameness that resolved with rest and anti-inflammatory drugs but recurred at 8 mo of age. Magnetic resonance imaging (MRI) of the lumbar, sacral, and coccygeal spine revealed a fluid-filled dilatation of the central canal of the spinal cord, which was interpreted as a hydromyelic cyst. Surgical exploration and drainage of the cyst were attempted. Despite initially improved mobility, severe plantar ulceration of both hocks developed. The animal was euthanatized. Gross necropsy of the central nervous system revealed a 1.5-cm-long, mild depression with associated yellowing of the dorsal spinal cord in the lumbosacral region, dilatation of the central spinal canal that extended from the cranial thoracic spinal cord with diameter increasing caudally, and mild herniation of the brainstem at the foramen magnum. Histopathologic lesions of the central nervous system were restricted to the spinal cord, with equivocal enlargement of the fourth ventricle. Pathologic changes included irregular dilatation of the central canal, flattening to the absence of the ependymal cells, spongiosis of the gray matter neuropil, and dystrophic calcification. The gross and histologic findings confirmed the diagnosis of hydromyelia.