The effect of osteoporosis, as diagnosed by bone densitometry, on general practitioners' decisions to initiate hormone replacement therapy (HRT) was assessed. Data for the study were collected by questionnaire from 147 women (> 40 years), previously referred for measurement of bone mineral density (BMD) at the proximal forearm. Among the women, at the time of BMD measurement, current and ever use of HRT was 35% and 50% respectively, and 25.2% were osteoporotic on the basis of their BMD level. HRT was more likely to be initiated by women who were told that their BMD was low (ODR 3.4; 95% CI 1.2-9.7); 37% of all women with osteoporosis were using HRT compared with 78% who were taking calcium supplements. Potential reasons for the low HRT prescription may include the nature of the BMD report, patient aversion to HRT and doctors' concern with the long-term side-effects of HRT.