The enormous global problem with tuberculosis with roughly one-third of the world's population infected with Mycobacterium tuberculosis, coupled with an increasing incidence of infections caused by nontuberculous mycobacteria, present unique challenges for the laboratory diagnosis of mycobacterial infections. Not only must the diagnosis of M. tuberculosis be optimized and expedited for good patient management and institution of appropriate control measures to prevent transmission of tuberculosis, but similar demands for accurate identification of the ever-increasing numbers of species of nontuberculous mycobacteria are also pressing for the laboratory. In light of these issues, the Clinical and Laboratory Standards Institute document M48-A-Laboratory Detection and Identification of Mycobacteria; Approved Guideline addresses topics related to the laboratory diagnosis of mycobacterial infections including safety and related issues, levels of service and referrals, clinical significance of mycobacteria, acceptable specimen types and their collection, transport and storage, specimen processing methods, methods for the direct detection of mycobacteria in clinical specimens, culture methods including contamination issues, reporting and quality control, and phenotypic and genotypic identification procedures.