Although Mycobacterium fortuitum is ubiquitous in our environment, infection of total knee arthroplasties with this organism is uncommon. This particular mycobacterium belongs to a group of organisms known as rapidly growing mycobacteria that distinguishes itself from the more typical Mycobacterium tuberculosis by their lower virulence and lack of human-to-human transmission. Another distinguishing feature is their resistance to almost all traditional anti-tuberculous medications and many antibiotics. Because such infections are encountered so infrequently, delays in reaching a microbiological diagnosis are not unusual. This inevitably compromises patient care. At present, there is no universally accepted treatment protocol. Management tends to be individualized, but cure may be possible with a prolonged course of appropriate anti-microbial therapy, removal of the implant, biopsy to confirm eradication of the organism, and finally, reimplantation of a new prosthesis. This paper presents the successful treatment of such an infection. Use of the combination of meropenem and moxifloxacin has not been previously reported in this setting. This case suggests that their in vivo activity is clinically effective against M. fortuitum peri-prosthetic infections when combined with surgical therapy.