A prospective study of fractures of the femoral neck was conducted over 12 months in order to ascertain the relevance of generalised osteoporosis as determined by metacarpal morphometry. A series of some 200 women sustaining a fracture of the femoral neck after minor trauma had bone mass measurements similar to those of a control population of normal women, and 16% were not osteoporotic. A history of previous fractures was documented in one third of the women, but this was unrelated to the presence or severity of osteoporosis, although over half of the fractures had occurred within the previous four years. Trochanteric fractures were seen more commonly in severely osteoporotic women (p less than 0.005), whereas cervical fractures predominated in those who were not osteoporotic. These findings support the hypothesis that postural instability is the major determinant for femoral neck fracture and that generalised osteoporosis, rather than being a prerequisite for fracture, merely determines the type of fracture sustained.