We present the 5-year results of the effect of adjuvant chemotherapy on bone mineral density (BMD) and the efficacy of clodronate in the prevention of bone loss in 73 premenopausal women with primary breast cancer. All patients were treated with cyclophosphamide, methotrexate, 5-fluorouracil (CMF) chemotherapy. The patients were randomised to oral clodronate 1600 mg daily for 3 years or to a control group. At 5 years, patients were divided into those with preserved menstruation and those with amenorrhoea. Changes in BMD correlated significantly with the menstrual function after chemotherapy. The change in the lumbar spine BMD at 3 and 5 years were +0.6 and -1.3% in the menstruating group and -7.5 and -10.4% in the amenorrhoeic group (P=0.0001 and 0.0001, respectively), and in femoral neck +1.7 and -0.3%, and -3.5 and -5.8% (P=0.002 and P=0.001, respectively). Three-year clodronate treatment significantly reduced the bone loss in the lumbar spine -3.0% compared with controls -7.4% at three years (P=0.003), but no significant difference was found in the femoral neck: -1.7% versus -2.8%, respectively (P=0.86). These differences between the study groups were still seen at 5 years: in the lumbar spine -5.8% versus -9.7% (P=0.008) and femoral neck -3.5% versus -5.1% (P=0.91). In conclusion, chemotherapy-induced ovarian failure in premenopausal women caused a temporary accelerated bone loss of the lumbar spine. Adjuvant clodronate treatment significantly reduced this bone loss. Two years after the termination of treatment, the bone loss was still significantly less in the clodronate group compared with the control group.