X-chromosome inactivation (XCI) is a process involved in the pathogenesis of several diseases. In this mini review, we discuss the known mechanisms associated with XCI, when and how does it initiate, spreads and maintain, as well as the mechanisms that allow some genes to escape from it. We address the skewed XCI, condition in which the process are not fully randomized and its consequences to the phenotype of some pathologies. We debate about the known pathologies implicated, including X unbalanced rearrangements, X-autosomal balanced translocations, Turner and Klinefelter syndromes and also for X-linked diseases and its consequences in males and females. Some pathologies are discussed more in detail such as intellectual disability with a recognized relationship with XCI. Finally, possible future implications of genomic therapy and treatment of patients and list of areas that need further research on this topic are addressed.