Mycoplasma hominis and Ureaplasma urealyticum are members of the Mycoplasma genus that can infect surgical wounds. These organisms are rarely cultured by conventional laboratory techniques, and they respond poorly to commonly used broad-spectrum antibiotics. Including this case, five cases of Mycoplasma mediastinitis have been reported, three of which followed heart-lung transplantation. Successful treatment of Mycoplasma mediastinitis after heart-lung transplantation was achieved in this patient with extensive debridement, muscle-flap coverage, and long-term antibiotics. Possible sources of this infection after heart-lung transplantation and treatment options are discussed.