Ultrasound as a diagnostic method is extremely important and in many cases it represents an irreplaceable new technique in modern medicine. Objectives: the aim of this research is to evaluate ultrasound examinations in rheumatological diagnostics, especially in the early detection of changes in the locomotor system in rheumatic patients, above all the changes occurring on the articular cartilage. This research helps us to define the degree of importance of ultrasound in clinical examinations of patients and to verify up to which point ultrasound is suitable to replace some other examination methods, applied more frequently in recent times. Patients and Methods: 32 patients with a swollen knee (30 with inflammatory rheumatism, 2 with undefined synovitis) were examined by ultrasound and results compared with the radiological ones, while in a smaller number of patients they were compared with the arthroscopy results. We use short ultrasound impulses that consist of a broad spectrum of frequencies for diagnostic purposes. The medium frequency of this spectrum is the so-called operating frequency. We use the ultrasound apparatus Siemens Sonoline Versa PRO and the ultrasound transducer of frequencies from 7.5 MHz. Results: a greater number of data about the pathological substrate were obtained in 53% of cases. Due to the ultrasonic statement, in 4 patients the diagnosis was modified, whereas in 4 patients a completely different diagnosis was made. After the ultrasonic examination 1 patient was sent to make additional examinations. The sensitivity of the ultrasonic examination was 86%, the specificity was 75% while the accuracy amounted to 85%. Conclusion: the research work has helped us realise that the diagnostic ultrasound has taken its undisputable place in the rheumatological department. This diagnostic method, however considerably, depends on the examiner’s experience. The experienced examiner, especially if using an ultrasound device with a high resolution, is able to make or complete a diagnosis with a great certainty. In some cases ultrasound can replace the radiological examination.