The design of eLearning systems aimed at personalizing the learning process, and which are based on given learning and cognitive styles, implies, from the teaching perspective, a need for evaluating potential teaching environments adapted to the preferences and forms of information processing of the students. In order to systematize this task, we have developed a methodology METHADIS which, based on a leaning objective, and by means of following a sequence of steps, determines instructional strategies custom-design for the specific needs of different users. Thus the contents, information formats, and activities are presented as a function of the learning styles; the helps and navigational options are given as a function of the specifics of each cognitive style. METHADIS was applied to a case of study where performance was compared between students in an experimental group which interacted with a hypermedia system design using this methodology and that of a control group.