Benign lymphoma, also referred to as a pseudolymphoma or as a benign lymphoid hyperplasia (BLH), is a rare non-cancerous (benign) tumor made up of lymphocytes. Lymphocyes or white blood cells are part of the body's immune system and help defend our body against infection. Lymphocytes circulate in our blood vessels as well as the immune systems own network of vessels and lymph nodes called the lymphatic system. Sometimes the lymphocytes grow abnormally and form tumors or lymphomas. Benign lymphomas are almost never life threatening, although they may grow and press against other tissues. Benign lymphomas and malignant (cancerous) lymphomas appear very similar under the microscope. This makes it difficult to diagnose benign lymphomas, and often leads to treatment for them in case they are, or will develop into, malignant lymphomas. Treatment often includes surgery to remove the tumor. Research studies are underway to discover ways to determine if a lymphoma is benign (harmless) or cancerous and to better understand those the course of benign lymphomas.