OBJECTIVE: Alendronate sodium (ALN) increases bone mineral density (BMD) in heterogeneous populations of postmenopausal women, but its effect is unknown in women with type 2 diabetes. The objective of this project was to compare changes in BMD during 3 years of ALN treatment versus placebo in diabetic women. RESEARCH DESIGN AND METHODS: We used data from the Fracture Intervention Trial, a randomized blinded placebo-controlled trial conducted at 11 centers in which 6458 women aged 54-81 years with a femoral neck BMD of <or=0.68 g/cm(2) were randomly assigned to either placebo or 5 mg/day ALN for 2 years, followed by 10 mg/day for the remainder of the trial. BMD was measured by dual-energy X-ray absorptiometry. Type 2 diabetes (n = 297) was defined by self-report, use of insulin or other hypoglycemic agents, or a random nonfasting glucose value >or=200 mg/dl. RESULTS: In diabetic women, 3 years of ALN treatment was associated with increased BMD at all sites studied, including 6.6% at the lumbar spine and 2.4% at the hip, whereas women in the placebo group experienced a decrease in BMD at all sites except the lumbar spine. The safety/tolerability of ALN was similar to placebo, except for abdominal pain, which was more likely in the ALN group. CONCLUSIONS: ALN increased BMD relative to placebo in older women with type 2 diabetes and was generally well tolerated as a treatment for osteoporosis. Increases in BMD with ALN therapy compared with placebo were similar between women with and without diabetes.