Solitary fibrous tumor and desmoplastic small round cell tumor are primary peritoneal malignant tumors. Despite their morphological differences, these diseases are united by low morbidity, the lack of pathogenic symptoms, similar radiological signs, and scant knowledge of prognostic factors. Considering the low morbidity, reliable differential diagnostic signs have not been established at present, which greatly complicates the timely formulation of the diagnosis. On the contrary, cases of choosing the wrong treatment tactics and the lack of a unified management algorithm are increasingly being identified. Radiation and instrumental diagnostic methods such as computed tomography, magnetic resonance imaging, laparoscopy are crucial in determining the extent of the tumor, it is necessary to take into account the biological characteristics of the tumor (morphological type), which affect the nature of tumor growth. With a solitary fibrous tumor and a desmoplastic small-round cell tumor, the computed tomography picture is characterized by the presence of isolated nodular formations in any part of the abdominal cavity, which can also be accompanied by a large omentum, ascites, an increase in retroperitoneal lymph nodes, and distant metastasis to the lungs and bones is possible. In general, the main task of diagnosing a primary peritoneal neoplasm is to take sufficient quality biological material, with the leading role in the diagnosis being given to histological and immunohistochemical studies. On the other hand, the independent experience of many clinics does not exceed single surveillance. This information does not allow doctors to confidently navigate the problem; accordingly, there is a need for multicenter and, possibly, prospective, randomized scientific research in order to develop a unified algorithm for managing patients with primary peritoneal tumors. The approaches to the treatment of these tumors are currently not standardized and not well studied due to the rarity of the pathology. According to the available information, the treatment of desmoplastic small round cell tumors is based on multimodal therapy, including systemic chemotherapy and surgery, and possibly radiation therapy. Traditional treatment algorithms for this pathology include the surgical stage and systemic or intracavitary chemotherapy, while the treatment sequence may be different and depends primarily on the prevalence of the disease. For solitary fibrous tumor, surgical treatment, by contrast, is the method of choice. Thus, when choosing a treatment strategy for a primary peritoneal tumor, it is first of all necessary to take into account the morphological type of the tumor and rely on known data on the benefits of a particular method. In this article, we tried to present modern information on the diagnosis and treatment of rare forms of primary peritoneal tumors.