Proteus morganii (Morganella morganii) is an uncommon cause of septic arthritis. We describe a 53-year-old woman with severely deforming rheumatoid arthritis, who developed an indolent septic arthritis secondary to infection with this organism. She was treated with antibiotics and closed drainage, and subsequently, underwent successful arthroplasty. She continues to do well 4.5 years later. This patient's disease course shows that gram-negative septic arthritis, effectively treated, does not preclude successful total joint arthroplasty.