Early diagnosis and prompt, effective treatment is the basis for the management of malaria and key to reducing malaria mortality and morbidity. An acceptable microscopy service is one that is cost-effective, provides results that are consistently accurate and timely enough to have a direct impact on treatment. This requires a comprehensive and active quality assurance (QA) program. This manual outlines a hierarchical structure based on retraining, validation and the development of competency standards designed to ensure the quality of diagnosis necessary for a successful malaria program, while remaining within the financial and personnel resources likely to be available. The mode of implementation of the QA system outlined in this manual will vary according to the organization of the national laboratory services dealing with malaria, which may fall under the national malaria control program, or under a separate laboratory structure working closely with the malaria program.