The results of endoscopic stomach drainage of fluid aggregates and post-necrotic pancreatic cysts have been investigated in 34 patients. All the patients were divided into two groups. The first group included early stage patients (from the onset of the disease up to 6 weeks duration), the second group covering the period post 6 weeks. According to the findings of the histological examination of pancreatic site tissue and peripancreatic fiber specific features of forming post-necrotic pancreatic cysts at early and late stages from the beginning of the disease have been studied by means of the endoscopic ultrasound technology. Besides, the stages of post-necrotic pancreatic cyst formation have been explored. The technology of through-the-stomach drainage has been developed, including the cyst puncture at the initial phase as well as subsequent dissection of the stomach wall and the cyst with the cystotome and its emptying. In the postoperative period balloon dilation of the cystogastroanastomosis and stage sanitations were carried out. If necessary, necrectomy with stent application was performed. Draining time parameters have been determined depending on the capsule formation, which consists of the early fibrinous layers and granulation tissue and subsequently turns into the fibrous membrane 3.4 mm thick. The study of the results of operations and the analysis of the causes of complications have been conducted, gastric bleeding being the most dangerous complication registered in 3 patients. To prevent intraoperative bleeding the method of post-necrotic cyst drainage has been changed.