The objective is to show superior efficacy of PTH (1-84) over risedronate in treating osteoporotic women for 12 months after having previously been treated with PTH (1-84) for 12 months followed by 12 months treatment with risedronate.

Inclusion Criteria:

Women above the age of 50 years with the diagnosis of postmenopausal primary osteoporosis may be enrolled in the trial if the following inclusion/exclusion criteria apply.

All inclusion criteria must be answered "yes" for a subject to be enrolled in the trial.

1. Has the subject given informed consent according to local requirements before any trial related activities? (A trial related activity is any procedure that would not have been performed during the routine management of the subject).
2. Is the subject above 50 years old?
3. Is the subject postmenopausal (more than 5 years) - in the judgement of the investigator?
4. Does the subject have primary osteoporosis with a lumbar spine T score < -3.0 SD (at lumbar spine L1-L4, with a minimum of two evaluable vertebrae)?
5. Does the subject have a life expectancy of >3 years?
6. Is the subject able to self-inject PTH (1-84), (or to have PTH (1-84) injection by a helper)?

Over three years of the trial duration.

The safety analysis set (SAF) was defined as all subjects enrolled in Trial Period I who received at least one dose of the IMP.

At each contact between the site and the subject (visit or phone) the subject was asked if she has experienced any health problems since the last contact.