The prevalence of mastocytosis is believed to have increased significantly in the past 15–20 years after the definition of the WHO diagnostic criteria, the development of more sensitive methods for detecting MC clonality (e.g., molecular methods for D816V KIT mutation, multiparametric flow cytometric analysis), the growing experience of physicians and pathologists and the creation of multidisciplinary centers specialized in this disease. This evidence concerns the gene KIT and mastocytosis.