The demand for open data has led to the creation and the availability of numerous portals releasing data. However, a large percentage of them are not properly designed for professional use. One way to analyze the value that a portal delivers is through its reputation, but this is a concept that has not yet been well defined or measured. This work will focus on the reputation of open data portals with two objectives. The first objective is to delimit the concept of reputation for open data portals, therefore leading to the first proposed research question: How can the reputation of open data portals be defined? The second objective is to propose criteria for measuring reputation and to create a reputation index for open data portals, with the second research question: How can the reputation of open data portals be assessed? This work is conceptual and descriptive and proposes a multidimensional definition of this concept, which includes whether it is known, being known for something, and its generalized favorability. In addition, a proposal is made for a reputation index identifying its dimensions and measurements, and finally, an analysis of its usefulness is presented. To this end, a figure has been created that summarizes the dimensions and benefits for creators and developers of open data portals and for the different application sectors (public, private, academic, and third sector). This research can help public administrations and other sectors to have a reference of good practices when offering open data to citizens and organizations oriented towards creating value in society.