Data from a prospective study were used to InvestIgate risk factors for hip fracture among a representative population of middle-aged adults. During the years 1974–1978, all women (n = 25,298) and men (n = 27,015) aged 35–49 years In three Norwegian counties were Invited to attend a cardiovascular screening (attendance rate = 91.5%). This cohort was followed throughout 1990 with respect to hip fracture, for a total of 572,006 person-years. A total of 281 new fractures were identified, of whIch 71 were excluded from the analysis due to high-energy trauma or fracture In metastatic bone. Age-adjusted relative risks (RR) and 95% confidence intervals (CI) for hip fracture increased with body height in women (RR = 3.62, 95% CI 1.46-8.97, ≥1.70 m vs. <1.55 m) and men (RR = 2.92, 95% Cl 0.94–9.05, ≥1 .85 m vs. <1.70 m). A history of diabetes mellitus also gave elevated risk of fracture (RR = 5.81, 95% CI 2.15–15.71 in women and RR= 7.67, 95% Cl 2.40-24.53 in men). In addition, hip fracture was related to body mass index (inverse), disability pension, and marital status. An Increased risk for smokers appeared only among those consuming <15 cigarettes per day. In multivariate analysis, all these risks remained elevated. This study suggests that, as In older populations, known risk factors for low bone mass are related to hip fracture among middle-aged adults. In addition, body height seems to have an independent influence on hip fracture incidence in this age group.