A 58-year-old woman presented to the emergency department with cauda equina syndrome and sepsis. The symptoms were attributed to a complicated episode of sigmoid diverticulitis. MRI showed that the diverticulitis had caused an intra-abdominal fistula to a presacrally localized abscess expanding into the spinal canal, compressing the cauda equina nerves. Although Hartmann's procedure was performed, the neurological symptoms persisted, causing the patient to remain partially paraplegic. This case report illustrates that cauda equina syndrome is a condition that can also be caused by intra-abdominal pathology such as diverticulitis.