PTH & Ibandronate Combination Study (PICS)

Inclusion Criteria: * Female * Aged 55-75 years, inclusive, at randomization * Postmenopausal for \>= 5 years (no menses for at least 5 years) * Have an evaluable bone mineral density scan (DXA) at the spine AND at the hip with a T-score \<= -1.5 either at the spine or the femoral neck or total hip OR have a T-score \<= -1.0 with at least one of the following risk factors for fracture: 1)Age \>= 65 years; 2)History of post-menopausal fracture (non-vertebral or vertebral); 3)Maternal history of hip fracture. * Be willing and able to self-administer daily injections * Signed written consent form. Exclusion Criteria: * History of more than 12 months of oral bisphosphonate use ever, or any use (\>4 weeks) with the past 12 months. For those with 4 weeks to 12 months of previous use, a 24 month washout is required. * History of any IV bisphosphonate use. * History of more than 12 month of PTH use ever, or any use (\>4 weeks) with the past 12 months. * History of estrogen (oral or patch) more than one month in the last 6 months or for more than 12 months in the last 2 years. * Have type 1 or uncontrolled type 2 diabetes mellitus (defined as hemoglobin A1C \> 10.0), or currently using insulin. * Have serum calcium \>10.2 mg/dl. * Have Vitamin D level \<15 nanograms/ml. * Have Stage III renal insufficiency where calculated creatinine clearance \< 40 ml/min by MDRD. * Have any history of kidney stones in the last 10 years. * Have any history of hypercalcuria or currently have urine calcium \>300 mg/24 hours. * Have any history of hypercalcemia. * Have any history of sarcoidosis. * Have any history of hyperparathyroidism. * Have any history of active or treated tuberculosis or other granulomatous disorders. * History of breast cancer, melanoma or hematologic malignancy which has required treatment within the last 10 years. * Any history of bone cancer or Paget's disease of bone * Any other metabolic bone disease which has required treatment within the last 10 years. * History of any other non-skin cancer which has required treatment within the last 10 years. * Have a documented history of symptomatic esophageal reflux, achalasia or esophageal stricture. * Be currently taking \> 7.5 mg systemic prednisone or equivalent per day or for more than 10 days in the last 3 months. * Be currently using \> 2 puffs, 4 times / day of inhaled steroids. * Be currently taking anticoagulants. * Be currently taking anticonvulsants that alter hepatic vitamin D clearance * Have used Calcitonin within the past 3 months. * Have used Raloxifene in the last 6 months or for more than 12 months in the last 2 years. * Have used Tamoxifen in the last 6 months or for more than 12 months in the last 2 years. * Have used fluoride for at least a month within the past 5 years. * Be currently taking \> 1000 IU/day Vitamin D * Using Vitamin D analogues or metabolites. * Be currently taking thyroid hormone replacement AND have a TSH \< 0.1mIU/L. * Have any major life-threatening illness. * Concurrent enrollment in another double-blinded clinical treatment intervention study. * Life expectancy less than 3 years * Willing to discontinue all over the counter nutritional supplements