Prolonged corticosteroid administration, as often required in the treatment of sarcoidosis, increases the risk of osteoporosis and fracture. The aim of the present study was to evaluate the usefulness of alendronate, a third generation bisphosphonate, in preventing corticosteroid-induced osteoporosis. Forty-three consecutive, previously untreated, sarcoid patients (17 men and 26 premenopausal women) were included in the study: 13 needed no treatment and served as controls (Group 1) and 30 needed glucocorticoids (prednisone) and were randomly selected to also receive either placebo (n = 15, Group 2) or alendronate 5 mg/day (n = 15, Group 3). Bone mineral density (BMD) at the ultradistal radius by dual photon absorptiometry (Osteograph 1000, NIM, Verona, Italy) and biochemical markers of bone turnover were measured at baseline and after 6 and 12 months of glucocorticoid therapy. No significant difference was found between Groups 2 and 3 in the mean cumulative dose of prednisone (4945 ± 1956 mg and 5110 ± 2013 mg, respectively). At the end of the study period, BMD increased by 0.8% in the alendronate-treated group; in the placebo-treated group, BMD decreased by 4.5%. The difference between groups was significant (P < 0.01, ANOVA). A significant decrease in markers of bone formation was found in all patients treated with prednisone (Groups 2 and 3), independently of alendronate. Alendronate, however, counteracted the increase in markers of bone resorption induced by glucocorticoid therapy. Our data suggest that alendronate is effective in preventing glucocorticoid-induced bone loss in sarcoid patients. Further studies on alendronate use in steroid-induced osteoporosis are needed.