Background: Еndoscopic neurolysis of the sciatic nerve has proven itself as a low traumatic and effective technique of treatment for deep gluteal pain syndrome and sciatic nerve neuropathy. Until now, there have been no publications dedicated to the parietal peritoneum damage after endoscopic sciatic nerve decompression. Clinical case description: A 70-year-old female patient with deep gluteal pain syndrome and sciatic nerve neuropathy on the right side and failure of a conservative treatment. According to the VAS scale, the severity of pain syndrome was 10 cm. The severity of the motor dysfunction, according to the BMRC scale, was 4 points. The severity of the sensitive dysfunction, according to the Seddon scale, was 3 points. The functional activity of the lower limb, according to the LEFS scale, was 48 points. The instrumental investigation of the sciatic nerve included MRI, ultrasound, and ENMG. Endoscopic sciatic nerve decompression was performed in the prone position with saline irrigation using the technique published before. After the surgery, an ultrasound study and a CT scan were performed, which determined the presence of a free fluid in the abdominal cavity, and edema of the right retroperitoneal space. The patient underwent laparoscopy, which revealed the area of the parietal peritoneum damage in the lower floor, with a free saline fluid detected in the abdominal cavity, which was evacuated. The patient was discharged from the hospital on the 10th day after the surgery. 6 months after the surgery, the functional activity of the lower extremity, according to the LEFS scale, was 52 points. Pain syndrome, according to the VAS scale, was 8 cm. The severity of the motor dysfunction, according to the BMRC scale, was 4 points. The severity of the sensitive dysfunction, according to the Seddon scale, was 3 points. The performed surgical endoscopic treatment was rendered ineffective. Conclusion: The method of endoscopic sciatic nerve decompression with saline pumping has a risk of the following complication: damaging the parietal peritoneum, saline penetration into the abdominal cavity, edema of the retroperitoneal space. To decrease the risk of this complication, it is necessary to observe the specific surgical conditions such as: controlled hypotension in a patient and a low pressure in the arthroscopic pump, the time of surgery not exceeding 1 hour, and the saline consumption not exceeding 10 liters. It is also crucial not to perform the dissection and neurolysis too proximal to the piriformis area.