Mycobacterium Fortuitum (M. Fortuitum) is a type of opportunistic pathogen commonly found in water/soil and belongs to the nontuberculosis mycobacteria (NTM) family. Prosthetic joint infection due to M. Fortuitum is extremely rare. We present a case of a 21-year-old female with an infection following a radical resection of the proximal tibia due to a parosteal osteosarcoma.