Introduction. Primary retroperitoneal tumors (TRPs) are tumors that develop in the retroperitoneal space of the mesenchymal, neuro-ectodermal, or vestigial tissues and have no organic or metastatic affiliation. TRPs are a heterogeneous morphological group, the definitive diagnosis being possible to establish only after histopathological and immunohistochemical examination. Aim of study. To carry out the importance of morphological and immunophenotypic aspects on retroperitoneal tumors in order to predict the neoplastic process. Methods and materials. The study is descriptive, prospective. The study group included 118 patients hospitalized for diagnosis and treatment with suspicion of TRP in the Gastrology Department of IMSP IO, during 2016-2020. Results. Out of 118 hospitalized patients, only in 84 cases what constituted (71.18%) proved to be primary. Liposarcoma was the most common histopathological form of malignant TRP, established in 20 cases which was (23.80%). The following, the most common, were non-Hodgkin's lymphoma with retroperitoneal lymph node involvement in 7 cases which constituted (8.33%), undifferentiated pleomorphic sarcoma - 6 cases (7.14%), leiomyosarcoma - 4 cases (4.76%) fibrosarcoma - 3 cases (3.57%), MPNST - 2 cases (2.38%), hemangiopericytoma, myofibrosarcoma, osteosarcoma, synovial sarcoma, ectopic seminoma - each with 1 case (1.19%). Although immunohistochemistry techniques were used, in 6 cases what constituted (7.14%) it was not possible to determine the morphopathological diagnosis. Among benign TRPs, the most common histopathological forms detected were benign lipoma and schwannoma 7 each (8.33%) and retroperitoneal cyst - 6 cases (7.14%). The rarest histopathological forms were: retroperitoneal lymphadenopathy - 3 cases (3.57%), mesenchymoma and neurofibroma (2 cases each (2.38%)), angiolipoma, fibrolipoma, granuloma, leiomyoma, lymphangioma (1 case each). constituted (1.19%). To finalize the histopathological diagnosis of TRP, immunohistochemistry techniques were used in 44 cases which constituted (37.28%). The use of immunohistochemical diagnostic techniques allowed the finalization of the morphopathological diagnosis of TRP in 30 cases which constituted (25.42%), and in 14 cases what constituted (11.86%) the non-TRP status of the tumors was confirmed, these being: metastases of carcinoma in 4 cases (3.39%), neuroendocrine tumor - 4 cases (3.39%), GIST - 5 cases (4.23%), peritoneal pseudomyxoma - 1 case (0.84%). Conclusion. The morphological aspect and the immunophenotype of the primary retroperitoneal tumors are defining characteristics in the predictive assessment of the evolution of the neoplastic process.