Vitamin D3 (or its physiologic equivalent, ergocalciferol), administered at a dose of 100,000 IU every 4 months for 5 years, is effective for primary prevention of fractures in the active elderly aged 65 to 85 years. This treatment regimen has no effect on cardiovascular, cancer, or all-cause mortality. Despite a seemingly large dose averaging 800 IU per day, this regimen is a safe, cheap (<$2 per year), and effective therapy for primary prevention of fractures.