A composite endpoint (CE) is a single outcome that combines various outcomes and measures the number of patients who present at least one of the individual components. The objective of this Master Thesis is to learn about the use of CE and develop a methodology to decide between a dichotomous primary endpoint and a composite one in terms of the asymptotic relative efficiency (ARE). A bibliographic research will be accomplished with the aim of seeing the use of Combined endpoints in HIV during 2012 to then, develop a statistical theoretical framework to get an expression for the ARE. Based on its values, statistical recommendations are given in the area of HIV to decide whether to expand a study primary endpoint to the composite, as well as preliminary results in other areas.