We report the case of a 70-year-old Japanese man who was referred from a local urologist because of acute urinary retention (detrusor underactivity revealed by a urodynamics examination). A neurogenic urinary retention workup failed to reveal the aetiology, but a spinal tap incidentally showed occult meningeal reaction with positive oligoclonal band. The patient had no headache, nausea/vomiting or fever. Considering his clinical laboratory findings, his neural lesions seemed to involve the meninges and spinal cord, suggestive of 'form fruste' meningitis-retention syndrome. When clinicians encounter patients with urinary retention of undetermined aetiology, a spinal tap should be considered.