Adaptive Hypermedia Systems are systems that adapt themselves according to the user’s profile. They are used in distance learning environments to adapt teaching materials and navigation to the user´s learning preferences. These systems support the learning process in a personalized manner, and they can be adapted to the Cognitive Learning Style (CLS) of each individual. This paper presents a diagnostic tool to the student's CLS active x Reflective dimension of Felder and Silverman’s model based on user´s interaction with asynchronous communication tools.