The role and possibilities of photodynamic theranostics, including fluorescence diagnostics and photodynamic therapy, in complex cytoreductive surgical treatment of peritoneal carcinomatosis, evaluation of the effectiveness of its use, and analysis of the impact of this approach on the results of surgical intervention were investigated. Available modern domestic and foreign scientific literature were analyzed using PubMed, eLibrary.ru, and Google Scholar. Peritoneal carcinomatosis is characterized by the spread of tumor cells in the peritoneum and can be either a primary form of a tumor, such as pseudomyxoma and mesothelioma, or metastatic spread of cancer, most often of the gastrointestinal tract or gynecological organs. Surgical treatment of peritoneal carcinomatosis is crucial in the complex treatment of this category of patients, which determines the importance of further improvement of cytoreductive technologies. The extent of peritoneal dissemination during surgery may be underestimated, since intraoperative diagnosis is based solely on visual inspection and palpation. Thus, the use of phototheranostics — fluorescence diagnostics and photodynamic therapy — is a promising direction that has an antitumor effect and visualizes the peritoneum involved in the oncological process, which is beneficial for determining the required volume of peritonectomy. Currently, they are promising methods in the treatment of tumors of various locations. Both techniques are linked by the principle of theranostics (including diagnosis of the disease and personalized treatment of the patient) and imply the use of specific dyes (photosensitizers) and their ability to be excited under the influence of light of a certain wavelength. The therapeutic and diagnostic potential of phototheranostics in the complex surgical treatment of peritoneal carcinomatosis is emphasized; the main problems are described and prospects for the development of this technology are presented based on retrospective and prospective studies and systematic reviews.