A newly designed ultrasonography probe is presented which can be advanced through the instrumentation channel of an operative endoscope (TGF-Olympus). The A-scan allows the differentiation between solid and cystic masses in the upper abdomen leading to gastric impression. Guided puncture of pancreatic pseudocysts is based on a solid diagnosis and can be performed from the gastric lumen thus avoiding the development of pancreato-cutaneous fistulas.