The mesentery and the omentum are the main fatty tissues in the abdomen. Various pathologic conditions such as benign and malignant neoplasm, inflammatory process, and traumatic lesions may involve the mesentery and the omentum. Differentiation of some lesions, whether they are in the mesentery or the omentum, is very important for accurate diagnosis and proper treatment. Vascular structures are important anatomical landmarks to determine the intraperitoneal fat plane accurately. The superior mesenteric artery and vein run through the small bowel mesentery. The middle colic artery and vein run through the transverse mesocolon. The sigmoid and superior rectal vessels run through the sigmoid mesocolon. Among various neoplastic diseases that involve the mesentery and the omentum, secondary neoplasms are more frequent than primary ones. Sclerosing mesenteritis, tuberculosis, and traumatic lesions may involve the mesentery. Tuberculosis, traumatic lesions, infarction, and torsion can occur in the omentum. Multidetector computed tomography (MDCT) images are valuable for the exact location of pathologic conditions by use of multiplanar reformatted images.