Magnetic resonance imaging (MRI) of cervical spine was performed in 16 patients of juvenile asymmetric segmental spinal muscular atrophy (JASSMA) in neutral and flexed positions to look for abnormalities in the spinal cord and the surrounding structures. The study included 5 normal individuals and 5 disease-negative controls who had spinal cord atrophy due to amyotrophic lateral sclerosis. In normal and disease-negative controls, lower cervical spinal cord moved forward and got mildly flattened against the vertebral bodies during flexion. The subarachnoid space increased behind the cord with no significant forward movement of the posterior dura mater; epidural space was just visible. The patients of JASSMA showed spinal cord atrophy in a small vertical segment in front of cervical 4 to 7 vertebral bodies. In addition, 9 patients had high cord signal on T2 weighted images, mainly localized to anterior and lateral horns of the grey matter. In flexion, there was marked anterior displacement and anteroposterior flattening of lower cervical cord against the vertebral bodies; posterior dura mater also moved forward obliterating subarachnoid space in all the patients. A large posterior epidural space was visible which showed enhancement after gadolinium-DTPA administration. Twelve patients had prominent blood vessels in this epidural space. These findings suggest that MRI done in neck flexion may have diagnostic significance in JASSMA.