The spleen has the same relationship to the circulatory system that the lymph nodes have to the lymphatic system. A wide range of diseases can affect the spleen. Pathologic conditions of the spleen can be classified into the following categories: congenital diseases (accessory spleen, polysplenia, and asplenia); trauma; inflammation (abscess, candidiasis, histoplasmosis, and sarcoidosis); vascular disorders (infarction, diseases affecting the splenic vasculature, and arteriovenous malformation); hematologic disorders (sickle cell disease and extramedullary hematopoiesis); benign tumors (cysts, hemangioma, diffuse hemangiomatosis of the spleen, and hamartoma); malignant tumors (sarcoma, lymphoma, and metastases); and other disease processes that affect the spleen diffusely (portal hypertension, Gaucher disease, and sickle cell disease) or focally (Gamna-Gandy nodules). New magnetic resonance (MR) imaging techniques have increased the role of MR imaging in detection and characterization of splenic diseases. MR imaging is an excellent tool for diagnosis and evaluation of focal lesions and pathologic conditions of the spleen.