The aim of this study was to assess whether early intermittent I.V. administration of disodium pamidronate can effectively achieve primary prevention of glucocorticoid-induced osteoporosis (GIOP). A total of 27 in- or outpatients who required first-time, long-term corticosteroid therapy at a daily dose of at least 10 mg prednisolone were studied. Patients were randomly selected to receive either pamidronate and calcium or calcium alone. Patients allocated to pamidronate treatment (pamidronate group) received a first intravenous infusion of 90 mg pamidronate simultaneously with the initiation of their steroid treatment. Subsequently, they received 30 mg pamidronate, intravenously, every 3 months, for as long as steroid therapy was continued. As with the control patients (calcium group), they were put on a daily 800-mg elemental calcium supplement given as calcium carbonate. Lumbar spine and hip (total and subregions) bone mineral densities (BMDs) were measured at the start and every 3-months by dual-energy X-ray absorptiometry (Hologic(R) QDR-2000). Over 1 year, the pamidronate group showed a significant BMD increase in the lumbar spine (3.6%), and at all sites of the hip (2.2% at the femoral neck). In the calcium group, a significant BMD reduction was registered at the lumbar spine (-5.3%) and at the femoral neck (-5.3%). Differences between the groups were significant at all sites measured. Intermittent intravenous pamidronate effectively achieves primary prevention of GIOP, as assessed by BMD measurements over 1 year.