We examined prospectively the associations of bone density and bone dimensions with risk of hip fracture using data from the first National Health and Nutrition Examination Survey and its three follow-up studies. A cohort of 1,489 white women age 45 years or older who received detailed medical examinations in the baseline survey in 1971-1975 were subsequently contacted in 1982-1984, 1986, and 1987. Bone density and hand bone dimensions at several sites were measured at baseline. Fifty incident hip fractures were identified during the follow-up studies. Using Cox regression analyses, we found a relative risk of 11 for women with bone density below the 5th percentile, compared with those above the 75th percentile (95% confidence interval = 2.2-58). Women with smaller external bone dimensions also faced increased risk of hip fracture (relative risk = 4.6 for dimensions below the 5th percentile vs above the 75th percentile; 95% confidence interval = 1.5-14). On the other hand, internal bone dimensions were not associated materially with hip fracture.