Although several studies have been published on the gut microbiota composition, they are mainly focused on bacteria. Therefore, the world of gut yeasts, the "gut mycome", is still unclear. Over the last years, brand new gut microbiota analysis techniques have been applied to the study of yeasts, with exciting results both in health and in disease. A therapeutic potential for many gastrointestinal and extra-intestinal diseases has been recognized for selected yeast strains, such as Saccharomyces boulardii. This narrative review represents an overview of the new evidences regarding the "gut mycome".