Clostridia species are rare causes of pleuropulmonary infections. This report describes an immunocompromised patient who had a renal transplant, had multiple risk factors for anaerobic pleuropulmonary infection, and developed an acute empyema with hydropneumothorax that was associated with Clostridium sporogenes bacteremia. Therapy included antibiotics and surgical drainage of the empyema. Species identification of clostridia can usually be limited to whether the species is perfringens or nonperfringens because the majority of clinically significant clostridial infections are caused by Clostridium perfringens. Increased cost and consumption of time limits the usefulness of species identification of nonperfringens species. However, the identification of clostridia species that are known to be associated with specific underlying diseases or known to have variable and unpredictable antibiotic susceptibilities may affect patient management. The role of the laboratory in identifying such anaerobic isolates is discussed.