Important advances have been achieved in recent years in adult mastocytosis. However, our knowledge about childhood mastocytosis is limited because invasive tests are not routinely performed in children. We ignore the frequency of systemic involvement in childhood mastocytosis, its outcome, and which are the main clinical and laboratory parameters associated with persistence into adult mastocytosis and its severity.Childhood mastocytosis is a clonal mast cell disease, with different activating mutations in the KIT gene discovered in most patients. Serum tryptase is the best marker for mast cell burden in children, and, at baseline, correlates well with the severity of symptoms in childhood mastocytosis. Systemic mastocytosis definitely may occur in children, but bone marrow studies to demonstrate a systemic involvement are not routinely performed nor recommended; it can be estimated that around 30% of children may have bone marrow involvement as demonstrated by showing aggregates of mast cells or by flow cytometry of mast cells expressing the aberrant CD25 marker.A new and improved classification of childhood mastocytosis is needed, and should be based on the correlation of clinical manifestations, morphology of mast cells in the skin, and the predicted outcome of the disease. The current classifications of childhood mastocytosis do not address any of these important issues.