Previous studies have shown that several types of stem cells can differentiate into insulin-secreting islet beta-cells and that these cells can reduce blood glucose in some trials, but there has been no report of a long-term follow-up. We assessed the long-term effects of the use of autologous bone marrow mononuclear cells in the treatment of type 2 diabetes mellitus (T2DM). Based on the willingness to receive implantation of bone marrow mononuclear cells, One hundred and eighteen patients with T2DM were divided into two groups; the patients in group I were treated with autologous bone marrow mononuclear cells and patients in group II were treated with insulin intensification therapy. Mononuclear cells from bone marrow were injected back into the patient's pancreas via a catheter. Patients were followed-up after the operation at monthly intervals for the first 3 months and thereafter every 3 months for the next 33 months, the occurrence of any side effects and the results of laboratory examinations were evaluated. There were no reported acute or chronic side effects in group I and both the HbA1c and C-peptide in group I patients were significantly better than either pretherapy values or group II patients during the follow-up period. These data suggested that the implantation of autologous bone marrow mononuclear cells for the treatment of T2DM is safe and effective. This therapy can partially restore the function of islet beta-cells and maintain blood glucose homeostasis in a longer time.