A 42-year-old male was admitted for right-sided sciatica with asymptomatic septic arthritis of the fifth toe of the right foot. He had a history of active chronic hepatitis C and septic arthritis of the fifth toe of the left foot. His symptoms included low back pain, poorly systematized right-sided sciatica, impairment of all forms of sensation in both lower limbs, absent ankle jerks, episodes of urinary retention, urgency, and painless septic arthritis of the fifth toe of the right foot. Roentgenograms showed a spina bifida occulta of L5 and a bony erosin in the distal interphalangeal joint of the right fifth toe. Distal denervation in the territory of L5 was demonstrated by the electromyographic study. Magnetic resonance imaging disclosed an area of high signal on T1 and T2 images, located within the spinal canal opposite L4 and suggestive of an intraspinal lipoma, as well as tethering of the spinal cord in an abnormally distal position. Antimicrobial therapy was effective in ensuring resolution of the infectious arthritis. The low back pain and sciatica responded to nonsteroidal antiinflammatory drug therapy and did not recur subsequently. Many patients who have roentgenograms taken to evaluate low back pain and sciatica are found to have a spina bifida occulta. This complex birth defect involving the spinal canal, meninges and spinal cord or cauda equina can cause neurologic and/or urinary symptoms in adulthood. Magnetic resonance imaging is essential in this situation to evaluate the spinal cord and to look for an intraspinal lipoma.