Intravenous pamidronate is frequently used for the treatment of osteoporosis in patients who cannot tolerate oral bisphosphonates. The aim of the present study was to compare the changes in bone mineral density (BMD) after 1 year of treatment with either oral alendronate or intravenous pamidronate in patients with osteoporosis. We studied 40 consecutive patients starting treatment for osteoporosis: 20 received oral alendronate 10 mg/day and 20 received intravenous pamidronate 60 mg/3 months. Patients were started on intravenous pamidronate in the case of intolerance (within 1 month of start of treatment) of an oral bisphosphonate or in the case of contraindications for an oral bisphosphonate. BMD (spine and total hip) was measured with dual X-ray absorptiometry (DEXA) at the start of treatment and after 1 year. The BMD of the lumbar spine increased by 4.0% (P<0.05 vs baseline) in both groups, and the BMD of the hip increased by 3.3% and 2.9% (P<0.05 vs baseline) in the alendronate and pamidronate groups, respectively. The increases in BMD of the vertebral spine and the total hip after 1 year are comparable in the alendronate and pamidronate groups. We conclude that intravenous pamidronate can be used successfully as an alternative treatment in patients with gastrointestinal intolerance of an oral bisphosphonate.