A 45-year-old woman was admitted due to severe headache and neck stiffness. She had visited a local clinic for back pain and received a lumbar nerve root steroid injection 10 days before admission. Computed tomography and magnetic resonance imaging showed psoas abscess, pneumocephalus, and subdural hygroma. She was diagnosed with psoas abscess and meningitis. The abscess and external ventricle were drained, and antibiotics were administered. Unfortunately, the patient died on hospital day 19 due to diffuse leptomeningitis. Lumbar nerve root steroid injections are commonly used to control back pain. Vigilance to "red flag signs" and a rapid diagnosis can prevent lethal outcomes produced by rare and unexpected complications related to infection. Here, we report a case of fatal meningitis after infection of the cerebrospinal fluid following a lumbar nerve root steroid injection.