BACKGROUND Proteus mirabilis is the second most common pathogen that causes urinary tract infections after Escherichia coli. In rare cases, it is associated with vertebral osteomyelitis. The underlying mechanism of this relationship may be related to the retrograde dissemination of bacteria through the paravertebral venous plexus. METHODS We report a case of an 80-year-old Taiwanese woman who had recurrent episodes of fever and chronic back pain for 1 year. All blood cultures were positive for P. mirabilis. Inflammation scans and magnetic resonance imaging revealed a previously undetected vertebral lesion between the seventh and eighth thoracic vertebra. She responded well to treatment with antibiotics, reporting considerable relief of back pain and no fever recurrence at the 4-month follow-up. CONCLUSIONS Chronic back pain is a common but often dismissed symptom among the older population; osteomyelitis should be considered in patients with recurrent fever or neurological symptoms. Old age, chronic renal failure, and diabetes mellitus are possible predisposing factors for osteomyelitis. Our findings suggest that long-term treatment with antibiotics is effective for osteomyelitis caused by P. mirabilis,, although surgery is required for abscess formation or serious vertebral destruction.