Chronic inflammatory sensory polyradiculopathy is a defined entity, frequently underdiagnosed, and potentially treatable. It must be suspected in patients with sensory ataxia, normal nerve conduction studies, and MRI with thickened lumbosacral nerve roots and gadolinium enhancement. We present the case of a 57-year-old man with marked sensory ataxia on his left leg. Examination showed normal strength, decreased knee and ankle jerks. Light touch and pinprick sensations were reduced below the knees. Vibration and joint position sense were absent at the feet. Nerve conduction studies were normal. Tibial sensory evoked potentials disclosed absent responses bilaterally. CSF was acellular with elevated protein. Lumbosacral magnetic resonance showed thickening of roots, with gadolinium enhancement. The patient was treated with IV-Ig, 2 g/kg, for 5 days with improvement of symptoms. The clinical course, elevated CSF protein, the evidence of root enhancement on the MRI, good response to immunotherapy, and the exclusion of other causes of sensory ataxia, were compatible with the diagnosis of chronic inflammatory sensory polyradiculopathy. To diagnose this disease the identification of isolated involvement of the sensory roots is required.