Mycoplasma hominis is a commensal of humans. The organism has been predominantly associated with infections of the genitourinary tract. Extragenital infections have been described in neonates, in women during the postpartum period, and in immunocompromised patients. Pneumonia caused by M hominis is very rare. This report describes the development of M hominis pneumonia in a lung transplantation recipient and underscores the difficulty in establishing the correct diagnosis and the need for early and aggressive treatment with appropriate antimicrobial agents to insure a good outcome.