The paper presents the results of complex radiation diagnosis of 118 cases of retroperitoneal tumors and tumor-like states, including 71 patients with tumors of mesenchymal origin, 7 with those of neurogenic origin, 6 with cysts, 9 with lymphogranulomatosis, 8 with retroperitoneal fibrosis, 12 with metastases, and 5 with hematomas. A wide complex of routine and up-to-date high-technology radiation diagnostic techniques was used to study the patients. The authors show the merits and dismerits of each technique. Greatest attention is given to the assessment of current techniques, primarily to ultrasonography (US) and computed tomography (CT). The studies have indicated that despite some specific features, many retroperitoneal tumors and tumor-like states bear similarities when various radiation methods are employed. The authors describe some syndromes which can be used to make a diagnosis. Despite the high capacities of US and CT in studying the normal and pathological structures of the human body, there are still great difficulties in differentiating different abnormalities when even the latest techniques are applied, these cases need paracentic aspiration or open biopsy.