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The principal clinical risk factors of osteoporosis were correlated with vertebral bone density measured by biphoton absorptiometry in 2,279 women referred to a menopause clinic. Age, age at puberty, the menopause and how long ago it had occurred, smoking and past history of osteoporosis were negatively and independently correlated with bone density. Early onset of the menopause significantly increased the risk of a low bone density as compared with a natural or surgical menopause occurring after the age of 45. In contrast, estrogen replacement therapy and excess weight decreased this risk after the menopause. Osteoarthrosis and 25 (OH) vit. D3 levels were positively correlated with bone density. These variables taken together in a multiple linear regression model were able to explain only 25 per cent of the variations in bone density between individuals, suggesting the predominant role of other factors not taken into account in our study, notably of a genetic and environmental nature. Before the menopause, none of the factors studied enabled prediction of the risk defined by a low bone density. Among women with one or more clinical risk factors correlated with bone density, 29 per cent in fact had low bone density, as compared with 20 per cent in the absence of such factors. In contrast, 54 per cent of women with a low bone density had no risk factor. The results of this study show that the exception of secondary causes of osteoporosis, the majority of so-called "risk" factors which can be assessed by history have only a minimal influence on bone density.(ABSTRACT TRUNCATED AT 250 WORDS)