This is a two part study (screening and treatment). The first part (screening) is designed to evaluate the percentage of patients missed in diagnosing osteoporosis by general practitioners (GP's). The second part (treatment) is designed to determine the preference by patients for the once monthly ibandronate or the once weekly alendronate.

A multi-centre, randomised, open-label, cross-over study to evaluate the percentage of false negative osteoporosis diagnoses using the standard case-finding procedure as described by the Dutch Institute for Health Care (CBO) and to determine the preference of adult osteoporosis patients between once monthly dosing of ibandronate (150 mg) and once weekly dosing of alendronate (70 mg).

Inclusion Criteria:

• Women registered with a GP, without a prior history of osteoporosis. According to a case-finding procedure, osteoporosis will be diagnosed or excluded.

Exclusion criteria:

• Abnormalities of the esophagus which delay esophageal emptying such as stricture or achalasia.
• Inability to stand or sit in the upright position for 60 minutes.
• Previous use of bone active agents (e.g. strontium, PTH).
• Significant medical condition which may preclude the patient's ability to complete the study.
• History of alcohol or drug abuse.
• Hypersensitivity to any component of the bisphosphonates alendronate and ibandronate.
• Administration of any investigational drug within 30 days preceding the first dose of the study drug.
• Serum total calcium > 10.5 mg/dL or < 8.0 mg/dL (equivalent to 2.63 mmol/L and 1.99 mmol/L).
• Osteoporosis by secondary causes, will be excluded especially when an isolated deformity of the vertebral body is detected during x-ray analysis.