The retroperitoneal fascial planes can be affected by various clinical disorders. In most of the cases retroperitoneal involvement occurs secondary to spread of a distinct underlying etiology. Herein we report two cases of primary retroperitoneal fasciitis diagnosed with imaging findings. The diagnosis of retroperitoneal fasciitis should be made by exclusion since various and more frequently encountered disorders including acute pancreatitis, duodenitis, pyelonephritis, and appendicitis may present with similar imaging findings.