To determine whether implantable insulin pump (IIP) therapy and multiple daily insulin (MDI) injections could equally attain improved blood glucose control, and to compare the 2 treatments with respect to reducing daily blood glucose fluctuations, reducing serious hypoglycemic insulin reactions, and improving patients' quality of life. Randomized clinical trial. Seven Veterans Affairs medical centers. One hundred twenty-one male type II diabetic patients between the ages of 40 and 69 years, receiving at least 1 injection of insulin per day and having hemoglobin A1c (HbA1c) levels of 8% or above. Intensive therapy (IIP or MDI) for 1 year. Hemoglobin A1c and blood glucose levels. Blood glucose levels declined to 7.96+/-1.08 mmol/L (143.4+/-19.5 mg/dL) and 8.30+/-1.52 mmol/L (149.6+/-27.4 mg/dL) (mean +/- SD) for IIP and MDI, respectively (P=.57). Hemoglobin A1c levels improved in both groups (time effect P<.001), to means of 7.54%+/-0.83% (MDI) vs 7.34%+/-0.79% (IIP). IIP reduced blood glucose fluctuations compared with MDI (P<.001), and reduced the incidence of mild clinical hypoglycemia by 68% (P<.001); IIP also eliminated the weight gain associated with MDI therapy and yielded better overall quality-of-life (P=.03) and impact-of-disease subscale scores (P=.05). Adverse events included 25% of subjects with episodes of insulin underdelivery due to microprecipitates of insulin within the pump. Intensive insulin therapy with IIP and MDI is effective in controlling non-insulin-dependent diabetes mellitus. IIP has significant advantages in reducing glycemic variability, clinical hypoglycemia, and weight gain, while improving aspects of quality of life.