• Lumbar spine volumetric trabecular bone mineral density (BMD) by quantitative computerized tomography (QCT) [ Time Frame: From baseline to 18 months ] [ Designated as safety issue: No ]
  

• Lumbar spine volumetric trabecular BMD by QCT [ Time Frame: At 6 months ] [ Designated as safety issue: No ]
  
• 3-D microstructure variables by high-resolution QCT (HR-QCT)in the 12th thoracic vertebra (T12) [ Time Frame: At baseline, 6 and 18 months ] [ Designated as safety issue: No ]
  
• Biomechanical variables by finite element analysis in the 12 thoracic vertebra [ Time Frame: At baseline and 18 months ] [ Designated as safety issue: No ]
  
• Areal bone mineral density at lumbar spine, femoral neck, and total hip [ Time Frame: 18 months ] [ Designated as safety issue: No ]
  
• Lumbar spine volumetric integral BMD by QCT [ Time Frame: 6 months, 18 months ] [ Designated as safety issue: No ]
  
• Serum aminoterminal propeptide of type I procollagen (PINP) [ Time Frame: 3, 6, 18 months ] [ Designated as safety issue: No ]
  
• Serum type I collagen degradation fragments [ Time Frame: 3, 6, 18 months ] [ Designated as safety issue: No ]
  
• Safety [ Time Frame: Throughout study ] [ Designated as safety issue: Yes ]
  

This study is a multinational, European, multicenter, randomized, open-label, active comparator controlled study with two study periods: a screening phase of up to 6 weeks, and an open-label treatment phase of 18 months. Approximately 100 adult men with osteoporosis associated with sustained glucocorticoid therapy will be enrolled into the study. Approximately one half of the patients (at all investigational sites) will be randomized to teriparatide 20 micrograms/day (given as a subcutaneous injection), and the other half randomized to risedronate 35 mg once weekly oral tablet. All patients will receive approximately 1000 mg/day elemental calcium and 800 to 1200 IU/day of vitamin D.