Fracture of the proximal femur (hip fracture) as a consequence of osteoporosis is an important public health problem. Its incidence, which rises with age, varies according to geographical location and race. There is no information concerning hip fracture in Switzerland, which is a Western country with a particularly aged population. During 1987, 361 patients with hip fracture were recorded in the University of Geneva Hospital, which is the main referral center for a population of about 376,000 inhabitants. This represented 94% of all hip fractures occurring in the region. A moderate trauma was reported in 329 cases (91.1%). The overall annual incidence was 96.1 per 100,000 population (146.9 for women and 39.8 for men). When only hip fractures following moderate trauma were considered, the incidence was 87.6 per 100,000 population (138.8 for women and 30.8 for men). Rare under the age of 65, hip fracture incidence increased exponentially in older subjects. The mean age of patients with hip fracture was 82.0 years in women and 75.7 years in men. The ratio of cervical to trochanteric fracture was 1.03 and 1.12 in women and men, respectively. The mean length of stay in the orthopaedic ward was 30.5 days, and the total costs amounted to 8.8 million Swiss francs for hip fracture associated with moderate trauma. Forty-seven percent of subjects were transferred to another hospital for recovery or rehabilitation. During the stay in the orthopaedic ward, the mortality rate was 8.2%. These results emphasize the high incidence and cost of hip fractures in a region of Switzerland where the population is particularly old.(ABSTRACT TRUNCATED AT 250 WORDS)