Endoscopic Ultrasonography, or EUS, has joined medical techniques of endoscopy with high frequency ultrasound technique, known as ultrasound. This removable achievement allows physician for microscopic tissue examination, not only in digestive system, but also in its surroundings by highly frequent technique. Endoscopic ultrasonography detects all kinds and nature of possible abnormalities, including and information, which are necessary for proper diagnosis and optimal treatment. In experience hands, EUS can detect abnormalities, which are undetectable during any other techniques of examination. EUS is applied from inside the body, near or even touching the examined surface, so the precise, highly frequent energy of showing the images can be used. The sonography, MRI, CT techniques must show the inner organs through outside surface of body, loosing the resolution during process. The superior resolution of EUS shows 5 layers of digestive tract, almost equally good as by microscope; none of other techniques allows showing of intestinal wall equally good as this one. By EUS liquid has been proved with 90% of precision in diagnosis of operative degrees of pancreas tumours. CT in this case has shows only 50% of precision. Highly skilled surgeons are aware of application of these diagnostics techniques in preoperative cases so the surgical removement of tumours is going to be more effective. The precision of EUS findings are of critical importance for the utilisation of maximum of new treatment having in mind that abnormalities could be diagnosed and characterised without operative intervention. To be able to focus on specific anatomic surfaces, there is need of great knowledge, skillfulness and praxis during the manipulation with EUS instrument. The years of experience are needed to be able to achieve high standard of expertise. The accuracy of results varies, depending on physicians diagnostic experience, sub-optimal results are not going to be a good guide during treatment planning. Endosonographist must be in position to document at least 80% of accuracy in diagnosis and determination of disease stage in order to achieve 30-60% changes in plans treatment.