Abstract
The work contains an example of application of Rough Set Theory to decision making – diagnosing Mitochondrial Encephalomyopathies (MEM) for children. The resulting decision support system maximally limits the indications for invasive diagnostic methods (puncture, muscle and/or nerve specimens). Moreover, it shortens the time necessary for making diagnosis. The system has been developed on the basis of data obtained from the II Clinic Department of Pediatrics of the Silesian Academy of Medicine (further referred to as the Clinic of Pediatrics).