Splenomegaly, sometimes of massive extent, occurs in a large number of hereditary diseases, some relatively prevalent and others, rare to ultra-rare. Because physicians are often unfamiliar with the less common disorders, patients may suffer because of diagnostic delay or diagnostic error and may undergo invasive, non-innocuous procedures such as splenectomy that are potentially avoidable were the correct diagnosis suspected. In this review article, we discuss the definition and clinical ramifications of “massive” splenomegaly and describe several rare genetic disorders that are sometimes associated with marked splenic enlargement as well as four additional hereditary “splenomegalic” lysosomal storage diseases (cholesterol esterase storage disease, Niemann-Pick C disease, acid sphingomyelinase deficiency disease, Gaucher disease) in which approved or promising experimental treatments should generally obviate the need for palliative splenectomy. We also summarize current concepts about the appropriate use of splenectomy in patients with β-thalassemia, hereditary spherocytosis and Gaucher disease and discuss surgical alternatives to classical total splenectomy for these disorders.