Certain diseases, although rarely seen by most pediatric hematologists, need nonetheless be recognized by members of our subspecialty. Furthermore, rare diseases often provide understanding of pathogenetic mechanisms that have implications for a much wider field. Three such diseases will be discussed by experts during this workshop: Autoimmune lymphoproliferative syndrome (ALPS), systemic mastocytosis and paroxysmal nocturnal hemoglobinuria (PNH). The presentations in this workshop will not only remind attendees of the prevalence, presenting symptoms, diagnositic work up and available therapies for these problems but also give everyone an update on the newest scientific insights in regards to pathogenesis and potential new therapies.