Active proliferation of nucleated cells in the bone marrow is a description of the degree of proliferation of nucleated cells in the bone marrow of a normal person. Nucleated cell proliferation in the bone marrow of normal individuals is active and is a normal phenomenon. According to the degree of active proliferation of nucleated cells in bone marrow, there are five clinical categories of bone marrow proliferation. There are five types: active proliferation in normal cases, markedly active proliferation or extremely active proliferation, and reduced proliferation or extremely reduced proliferation. Significantly active hyperplasia is seen when there is a decrease in red blood cells in the peripheral blood, or when there is hemolysis. The most likely cause of hyperplasia is a variety of hematologic malignancies, such as acute leukemia, chronic leukemia, etc. If the bone marrow is hypoproliferative or severely hypoproliferative, it is commonly associated with bone marrow hematopoietic failure, the most common disease being aplastic anemia. Therefore, it is normal for the bone marrow to have active nucleated cell proliferation.