Mastocytosis is rare, and is actually a heterogeneous group of diseases that may only involve the skin (urticaria pigmentosa) or that may have a systemic presentation with multiorgan involvement. The gastrointestinal (GI) tract can be affected and symptoms related to GI involvement are often nonspecific. The diagnosis of systemic mastocytosis with primarily GI presentation can be challenging and requires familiarity with this entity and a high index of suspicion. We report a case of systemic mastocytosis primarily diagnosed by the recognition of small intestinal and colonic involvement and review the diagnostic criteria, histopathology, and recent developments regarding this entity.