The objective of this study was to evaluate the technical quality of sputum microscopy carried out for diagnostic purposes in the Network of Tuberculosis Bacteriology Laboratories in Colombia. The National Central Reference Laboratory received 6 529 slides for reexamination from the network of 513 sectional, regional, and local laboratories, witch contributed 33.2%, 27.6%, and 39.2%, respectively, of the slides. These included all the positive (3 283) and negative (3 246) smears processed during a 4-month period. The reexamination was carried out by six laboratory workers who did not know the origin of the slides or the original diagnosis