This phase II trial is studying how well giving lenalidomide together with prednisone works in treating patients with myelofibrosis. Lenalidomide may stop the growth of myelofibrosis by blocking blood flow to the cancer. It may also stimulate the immune system in different ways and stop cancer cells from growing. Drugs used in chemotherapy, such as prednisone, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Giving lenalidomide together with prednisone may kill more cancer cells.