The purpose of this study is to evaluate the efficacy and safety of an investigational drug in postmenopausal women with osteoporosis. The primary hypothesis of this study is that in postmenopausal women with osteoporosis, oral monthly ibandronate, at doses of 100 mg and 150 mg, does not achieve persistence in reduction of bone resorption throughout the monthly dosing interval, as demonstrated by a larger change in the serum carboxyterminal crosslinked telopeptide of Type I collagen (CTX-I) log-transformed fraction from baseline four weeks post dose compared to one week post dose, during the third month of treatment, in the participants taking ibandronate than in the participants taking placebo.

Inclusion Criteria: -postmenopausal for at least 3 years, with osteoporosis at any of the following sites: [BMD > 2.0 standard deviations below young normal mean bone mass for the hip trochanter, PA lumbar spine (L1 to L4), total hip, or femoral neck based on the normative database provided by each individual manufacturer].

• willing to take study-supplied calcium and vitamin D supplement (or equivalent) and to discontinue any non-study calcium supplements for run-in period and the duration of the study. Exclusion Criteria: -pregnant or lactating, or of childbearing potential.
• participated in another therapeutic trial with an investigational compound within 30 days of randomization.
• history of hypersensitivity to any component of ibandronate tablets or has hereditary problems of galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption.
• an abnormality of the esophagus which delays esophageal emptying such as stricture or achalasia.
• unable to stand or sit upright for at least 60 minutes once a month.
• current use of illicit drugs, or history of drug or alcohol abuse within the past five years.
• has any of the following: hypocalcemia; any severe malabsorption syndrome; moderate or severe hypertension which is uncontrolled; new onset angina or myocardial infarction within six months of entry into the study; evidence for impaired renal function; organ transplantation; or other significant end organ diseases (genitourinary, cardiovascular, endocrine, hepatic, psychiatric, renal, hematologic, or pulmonary).
• history of or evidence of metabolic bone disease (other than postmenopausal bone loss).
• clinical fracture in the past year.
• is receiving or has received treatment prior to randomization which might influence bone turnover.
• is receiving or expected to receive during the course of the study any medication (other than study medication) which might alter bone or calcium metabolism, including Vitamin A in excess of 10,000 IU per day or Vitamin D in excess of 5000 IU per day, calcitonin, phenytoin, heparin, or lithium.