Laparoscopic sleeve gastrectomy is known to be a safe and effective procedure for treating morbid obesity and is performed with increasing frequency both in Europe and the USA. Despite its broad use, many questions about the remaining gastric tube diameter, its long-term efficacy, its effects on gastric emptying, and the hormones involved still remain to be answered. In order to use such a relatively new surgical procedure wisely, it is essential for every surgeon and physician to understand how sleeve gastrectomy acts in obesity and what its potential benefits on the patients' metabolism are. This review focuses on the most important pathophysiologic questions referred to sleeve gastrectomy on the literature so far, in an attempt to evaluate the different issues still pending on the subject.