A 78-year-old man, who had recently been suffering from abdominal distension, was originally operated on at our hospital in 2006 for a choriocapillaris adenoma of the ascending colon. Recently, he was examined in our hospital for abdominal distension, which showed extensive fluid occupancy in the abdominal cavity and was suspected to be a metastatic tumor, which was later confirmed to be a pseudomucinous tumor by puncture biopsy. Surgery was performed yesterday. Intraoperatively, extensive yellowish and bloody mucus jelly-like fluid was removed as much as possible from the tumor, which weighed about 5 kg. Two double-lumen drains were placed for postoperative intraperitoneal chemotherapy. Pseudomucinous peritoneal tumor (PMP) is a rare peritoneal tumor with an incidence of approximately 1 in 1 million per year. It is disseminated worldwide. First named by Werth in 1884, PMP is characterized by a large amount of mucus-like fluid in the peritoneal cavity and multiple mucoid masses in the peritoneum and omentum, which are known as the “jelly belly”. The possible pathogenesis is that the proliferation of the lesion leads to narrowing and occlusion of the appendiceal lumen, which increases the pressure in the appendiceal cavity and gradually expands and eventually ruptures, trapping the mucus and cells shed by the lesion into the abdominal cavity, where the cells continue to proliferate indefinitely and produce large amounts of mucus. There is still debate in female patients surrounding whether the ovary is another major source of PMP, and recent immunohistochemical and allelic analyses seem to be more supportive of the appendiceal origin hypothesis. Additional rare sites of origin continue to be reported, such as the colorectum, stomach, biliary system, and pancreas, with some PMP of unknown origin. the spectrum of disease encompassed by PMP varies widely in benign and malignant nature, and therefore the diagnostic term PMP is not a guide to the diagnosis, treatment, or prognosis of patients. Ronnett et al. classified PMP into 3 categories: (1) diffuse peritoneal adenomatous mucinosis (DPAM), characterized by a large amount of extracellular mucus containing only a few proliferating mucinous epithelial cells with no significant cellular anisotropy and with or without associated primary mucinous adenomatous lesions, this type is common in 59.7% of cases. (2) Peritoneal mucinous adenocarcinosis (PMCA), characterized by more abundant mucinous epithelial cells with structural features and cytologic characteristics of cancer, with or without associated primary mucinous adenocarcinoma lesions, accounting for 27.5%. (3) Intermediate type. This classification has prognostic significance, with age-adjusted 5-year survival rate of 84% in the DPAM group and only 6.7% in the PMCA group. PMP has fewer cellular components, relatively well-differentiated cells, few lymphatic and distant metastases, and good general status in most patients; therefore, PMP is mostly considered as junctional malignant. Most patients with PMP have an insidious onset, slow progression, and lack of specificity of symptoms, so they are often found accidentally when a diagnosis of appendicitis or ovarian tumor is proposed for caesarean section. There is a high rate of misdiagnosis and delayed treatment. Common signs and symptoms include abdominal pain (often similar to acute appendicitis), abdominal masses (in women mostly suspected as ovarian tumors), abdominal distention, progressive enlargement of abdominal circumference, nausea, vomiting, malaise, loss of appetite, new hernia (inguinal hernia is common), weight loss, and rare complications. Imaging is important in this disease. Ultrasound and CT are more frequently used and visible signs include mucus-like fluid as fatty density, fan-shaped indentation on the surface of the liver and spleen, massive ascites sign, small intestine divided and concentrated in the center of the abdomen (but with mostly normal internal diameter and no obvious compression changes), and especially omental pancake-like thickening and arcuate calcification are more suggestive. CEA, CA19-9, CA125, etc. may be elevated in PMP patients, especially CEA is important for PMP, and the significant elevation often indicates advanced lesions, high malignancy, not easily eradicated, easy recurrence, and poor prognosis. The follow-up of tumor markers after treatment has the significance of predicting recurrence. The typical PMP ascites is a large amount of mucus-like fluid with poor mobility, which is often not easily extracted by abdominal puncture. Some patients with PMP can also present with exudate without obvious mucus or even hemorrhagic fluid. Histological examination is the gold standard for diagnosis. Surgery is the treatment of choice for PMP, with reduction surgery being the most common procedure. This procedure is simple and easy to perform, with a relatively low incidence of complications, and is suitable for all patients with PMP. However, it is prone to recurrence. Radical surgery is the removal of all lesions to reduce recurrence and can achieve better treatment results. However, this surgical approach is time-consuming, complex, risky and has many complications. New surgical advances such as the use of laparoscopy and ultrasound-guided suction have also been reported recently. Other treatments include: radiotherapy, immunotherapy (intraperitoneal injection of a streptococcal preparation OK-432), mucolytics, photodynamic therapy (laser irradiation), etc., all of which are reported in a few cases and the clinical efficacy is difficult to evaluate. The disease is prone to recurrence, with approximately 50% of cases recurring within 2.5 years, and most patients with recurrence are PMCA. Harshen et al. 2003 reported an overall 5-year survival rate of 10%-75% for patients with PMP, with a mean of 50%, after pooling related cases. the Mayo center reported 5-year and 10-year survival rates of 53% and 32%, respectively, with a median survival period of 5.9 years.