This work has been realised to estimate the lifetime risk of osteoporotic fracture for Belgian men and women aged 50 and 60 years. Estimates were based on a microsimulation Markov model. They take account of the incidence of fracture as well as of life expectancy. Several approaches have been taken to model life expectancy. Our estimates also take account of future mortality reductions based on official estimates and secular trends in life expectancy. Lifetime risk of osteoporotic population (bone mineral density below -2.5 T-score) was also estimated. Lifetime risk of hip fracture and any major osteoporotic fracture (hip, clinical vertebral or wrist) were 20.5% and 39% respectively for women aged 60 years. Corresponding values for men were 7.9% and 14.8% and for osteoporotic women 32.3% and 53.4%. Our lifetime risk estimates re-emphasize that osteoporosis is a major public health problem and that its societal burden is likely to increase due to demographic changes.