We reported a case in which cervical myelopathy exacerbated 20 years after the stabilization of juvenile muscular atrophy of unilateral distal upper extremity. The patient presented progressive weakness in the right proximal upper extremity and spastic paraparesis in addition to the long-lasting muscular atrophy of right distal upper extremity. Plain x-ray showed severe cervical spondylosis with kyphosis of the cervical spine. Dynamic study on MRI disclosed cervical spinal cord atrophy and compression enhanced in both flexion and extension position of the neck. Malalignment (kyphosis) and severe spondylotic change of the cervical spine seemed to affect the spinal cord with little functional reservoir, manifesting the delayed exacerbation of myelopathy. We conclude that malalignment and subsequent spondylotic change of the cervical spine would be significant factors to determine the long term prognosis of patients with juvenile muscular atrophy of unilateral distal upper extremity.