Inclusion Criteria:

1. CF; confirmed by a positive sweat test or DNA analysis
2. age 18 years or above at the time of informed consent
3. osteopenia (-2.5< BMD t-score<1.0) or osteoporosis (BMD t-score <-2.5)t-score at the LS (1-4)or total hip
4. provision of informed consent

Exclusion Criteria:

1. endoscopy-proven esophagitis, gastritis, ulceration, or abnormalities of the esophagus which delay esophageal emptying such as stricture, achalasia, or esophageal varices
2. significantly impaired renal function; this is defined as serum creatinine >177 umol/L
3. current or recent (within 1 year prior to randomization) consumption of an excess of alcohol or abuse of drugs; an excess of alcohol is defined as more than four of any of the following per day, or a combination of more that four of the following per day: 30 mL distilled spirits, 240 mL beer, or 120 mL wine
4. history of prior organ transplantation
5. any condition which may interfere with the evaluation of LS BMD as determined in a screening radiograph by a radiologist at the central facility e.g. spinal fusion, confluent aortic calcifications, surgical artefact, excessive osteophytes, or other permanent artefact; hip prostheses or any other condition that may interfere with the evaluation of hip BMD
6. participation in another clinical trial 30 days prior to enrolment or within 6 half-lives of the study drug if applicable
7. pregnancy, lactation, or a desire to become pregnant; safe effective birthcontrol must be used
8. know hypersensitivity or abnormal reaction to study drug or other bisphosphonates
9. use of drugs know to affect bone within 6 months of starting trial medication (e.g. thiazide, diuretics, calcitonin, calcitriol, anabolic steroids, estrogen or estrogen-related drugs (e.g. tamoxifen, raloxifene, tibolone high dose vaginal estrogen), progesterone, fluoride: this does not include the birth control pill
10. patients currently receiving another bisphosphonate in whom treatment efficacy has been established; only patients who are intolerant to or did not respond to another bisphosphonate will be considered for inclusion; patients must have ceased treatment with any bisphosphonate for at least 1 year prior to enrolment
11. use of systemic corticosteroids at a dose of at least 7.5 mg/day or greater within last 6 months
12. concomitant use of any investigational drug other than the study medication
13. current or recent (within 1 year prior to randomization) metabolic bone disorders other than secondary osteoporosis, such as Paget's disease, renal osteodystrophy, osteomalacia (25-OHD<25nmol/L), hypoparathyroidism, hyperparathyroidism; TSH outside normal laboratory range, with values that are assessed as clinically significant by the investigator; if on replacement therapy, dose should be stable and TSH within normal range for a minimum of 6 weeks prior to trial enrolment
14. hypocalcemia from any cause, corrected for low albumin
15. any history of cancer; for relatively benign skin malignancies, such as basal cell carcinoma or squamous cell carcinoma and patients with a history of successfully treated cervical carcinoma in istu, a documented six-month remission is required before study entry
16. poor medical or psychiatric risk for treatment with an investigational drug