Clinical microbiology laboratories play a critical role in diagnosing tuberculosis (TB) and monitoring its treatment. Poor quality laboratory services remain a major barrier to diagnosis by microscopy and culture, and may complicate the interpretation of drug susceptibility testing (DST) results. External quality assessment (EQA) for microscopy is an important component of quality assurance, and includes panel testing, slide rechecking, and on-site supervision. Periodic panel testing is the simplest way to assess the performance of laboratories. Rechecking of a sample of routine smears by a higher-level laboratory is the method of choice for evaluation and continuous motivation of peripheral laboratories. On-site supervision allows the observation of workers’ performance under actual conditions, including equipment handling, laboratory safety, adequacy of supplies, and the processes used for smearing, staining, reading, recording, and reporting. Culture performance is not easily measured, and existing EQA programs are not sensitive enough to estimate the sensitivity of the process. Therefore, laboratory regulations and accreditation programs are critical to assure the quality of cultures. The Supranational Reference Laboratory Network (SRLN) was organized in 1994 to ensure optimal performance of laboratories conducting DST. A panel of 30 pretested and coded isolates is exchanged annually within the network for proficiency testing. It has been demonstrated that education and an EQA program can improve the proficiency of TB laboratories. However, quality programs in Korea are still weak. Expanded and strengthened laboratory quality improvement systems are necessary to achieve TB control in this country. (Korean J Clin Microbiol 2009;12:147-153)