A 44-year-old woman was admitted to our hospital because of meningitis, with symptoms of an altered mental state and flaccid quadriparesis. Neurological examination revealed nuchal rigidity, flaccid quadriparesis without tendon reflexes, septic rash and urinary retention. Nerve conduction studies showed diminished F-wave ratios. However, the amplitudes and conduction velocities for bilateral motor and sensory nerves of the upper (medial and ulnar nerves) and lower (posterior tibial and sural nerves) limbs were all normal. Spinal MRI showed gadolinium enhancement of the bilateral sacral nerve roots, indicating radiculitis. In addition, T2*-weighed MRI of the brain revealed multiple microbleeds. Infectious endocarditis was detected on admission, and Staphylococcus aureus infection was confirmed by blood culturing. The patient was diagnosed with meningoradiculitis caused by S. aureus. Although antibiotic therapy did not improve quadriparesis, administration of dexamethasone led to a marked amelioration of the quadriparesis with a resultant complete recovery of the limb muscle powers in three months. Furthermore, as the quadriparesis improved, F-wave ratios gradually returned to normal and hearing loss remained as the only sequela. Therefore, adrenocorticosteroid therapy attenuated radiculitis-induced quadriparesis. Although radiculitis due to S. aureus is extremely rare, it should be considered because delayed treatment can lead to permanent injury and impairment.