CT scans of 54 patients with primary peritoneal soft tissue masses were studied retrospectively. All lesions were untreated at the time of the CT examinations and the nature of the lesions was subsequently proven histologically. Each scan was evaluated initially without knowledge of clinical and pathological information in respect of several criteria including size and number of lesions, delineation of the lesions, border definition, and internal structure of the lesions. The lesions were demonstrated in all patients and displayed with great anatomical detail. The presence of gas and attenuation values below -30 HU were the only singular signs specifically indicative of abscesses or lipomatous tumors, respectively. All other applied criteria were found both in sarcomas and benign masses, and no malignant neoplasm had CT characteristics specific enough to differentiate it from any other one. Considering all criteria, the benign or malignant nature of the lesions could be predicted in 43% of the patients studied based solely on CT morphology. In context with the clinical information provided on the study request form, 54% of the lesions were correctly classified into aetiological sub-groups (i.e. soft tissue sarcoma, abscess).