The spleen represents a major lymphatic and hematologic organ and, as such, is frequently involved in hematologic malignancies. Splenomegaly may constitute the first clinical sign leading to the diagnosis of a hematologic malignancy. Vice versa, the presence, or suspicion of a hematologic malignancy requires investigation of the spleen. In case of splenomegaly of unknown origin, directed history, clinical examination, and laboratory testing including a complete blood count with microscopic investigation of a peripheral blood smear, frequently allow to establish a tentative diagnosis. Whenever possible, further specific testing should be based on a thorough primary evaluation to avoid unnecessary diagnostic procedures. In light of the current diagnostic options, diagnostic splenectomy can usually be avoided to establish definitive diagnosis. Indolent lymphomas (chronic lymphocytic leukaemia, hairy cell leukaemia, splenic marginal zone lymphoma) and myeloproliferative neoplasms (chronic myeloid leukaemia, polycythemia vera, essential thrombocythemia, primary and secondary myelofibrosis) are the most prevalent hematologic malignancies associated with splenomegaly. Therapeutic options are highly differentiated depending on the underlying disease. Apart from very rare exceptions, therapeutic splenectomy can usually be avoided.