The differential diagnosis of upper intestinal obstruction includes mechanical obstruction, obstruction secondary to systemic disease, and idiopathic intestinal pseudo-obstruction. The causes of these are extensive; however, the majority of cases involve a mechanical etiology. Superior mesenteric artery syndrome (SMAS) is a rare and controversial form of mechanical obstruction with just over 300 well-defined cases described in literature. The diagnosis is often difficult to establish, even after surgery. In addition, this syndrome sometimes may be managed conservatively, leaving a definitive diagnosis unproven. A case of SMAS and a description of the syndrome is presented. The patient was managed conservatively and recovered without difficulty. One of the most difficult diseases to differentiate from SMAS is megaduodenum (intestinal pseudo-obstruction localized to the duodenum). Both entities present as obstruction with an unclear etiology. A reasonable approach to the diagnosis and management of upper intestinal obstruction (including figures, tables, and an algorithm), with emphasis on the above two diseases, is discussed.