The internal control of quality in the clinical laboratory is a specialized activity that monitors the quality of the processes and results at the same time that it allows to accept or to reject the analytic runs on the different determinations. To such effects, the elements of a practical guide included in a software are presented, designed with the objective of perfecting the internal control of the quality in these laboratories, where the principles and key concepts of the topic, procedures and their sequence, requirements of quality, control rules, statistical calculations, the interpretation of the results are defined, as well as some of the novel and necessary indicators to assure the quality. [ABSTRACT FROM AUTHOR]