This paper aims to report the complete absence of the superior mesenteric artery (SMA) in an adult and to propose a new classification method for the superior-inferior mesenteric arterial variations (SIMAV). A 69-year-old female was referred for abdominal pain and change of stool habits and characteristics. Multi-detector computed tomography (MDCT) was performed. Based on the CT findings of the patient and previous reports on the abnormalities of the superior-inferior mesenteric arteries, attempt was made to propose a new classification method for SIMAV. MDCT with enhancement revealed complete absence of SMA and compensatory dilation of the inferior mesenteric artery (IMA). Aneurysm of the splenic artery and both inferior phrenic arteries aberrantly arising from the aorta at the same level of the celiac trunk were also noted. Based on our case and literature reports, we were able to propose a new classification method for SIMAV. Without considering the relationship with the celiac arteries, SIMAV can be divided into 4 types. Type I is the normal type or "textbook" type. In type II, SMA is defective and in type III, IMA is defective. In type IV, there is an aberrant middle mesenteric artery (MMA). Complete absence of SMA is extremely rare. However, awareness of such a variation is of great importance during operations for rectal and sigmoid cancer. In such patients, ligation of the trunk of IMA, which is the only artery for the entire intestine, will lead to disastrous consequence. The new classification method may be helpful in the scientific and systematic description of SIMAV.