This study attempted to address the following questions: for an individual who is at present nonosteoporotic, given their current age and BMD level, what is the individual's risk of fracture and when is the ideal time to repeat a BMD measurement? Nonosteoporotic women (n = 1008) and men (n = 750) over the age of 60 in 1989 from the Dubbo Osteoporosis Epidemiology Study were monitored until one of the following outcomes occurred: (1) BMD reached "osteoporosis" level (i.e., T-scores < or = -2.5) or (2) an incident fragility fracture. During the follow-up period (average, 7 yr), 346 women (34%) and 160 men (21%) developed osteoporosis or sustained a low-trauma fracture. The risk of osteoporosis or fracture increased with advancing age (women: RR/10 yr, 1.3; 95% CI, 1.1-1.6; men: RR/10 yr, 2.3; 95% CI, 1.7-2.9) and lower BMD levels (women: RR per -0.12 g/cm(2), 3.2; 95% CI, 2.6-4.1; RR per -0.12 g/cm(2), 2.6; 95% CI, 2.0-3.3). Using the predicted risk (of osteoporosis or fracture) of 10% as a cut-off level for repeating BMD measurement, the estimated time to reach the cut-off level varied from 1.5 (for an 80-yr-old woman with a T-score of -2.2) to 10.6 yr (for a 60-yr-old man with a T-score of 0). These results suggest that, based on an individual's current age and BMD T-score, it is possible to estimate the optimal time to repeat BMD testing for the individual. The prognostic model and approach presented in this study may help improve the individualization and management of osteoporosis.