The effectiveness of elcatonin was assessed in a prospective study of patients with a diagnosis of postmenopausal/senile osteoporosis. In the first stage, 521 patients (490 women mean time since menopause, 14.4 years and 31 men; mean age, 61.4 years) with clinical evidence of osteoporosis were recruited. Bone mineral density (BMD) was measured in 486 of the patients, and pain and ability to function were assessed. In the second stage, the patients whose results for lumbar BMD were lower by 1 standard deviation than the peak bone mass of the normal reference population were treated with 40 U of parenteral elcatonin daily for 10 consecutive days and then on alternate days for the remaining 20 days of the first month, and in subsequent months for only the first 10 days of the month. A supplement of 1 g/d of oral calcium was recommended. Clinical examination was done at the beginning of the study and then at 3-month intervals. Densitometry was performed at the start and after 6, 12, and 24 months. The data were collected by 48 specialists, each of whom chose a group of patients who had not been treated for osteoporosis in the previous year. A total of 130 patients completed a year of treatment with elcatonin; 67% of these were responders, as shown by an increase of 3.53% in lumbar BMD using analysis of variance ( P = 0.001). According to Wilcoxon's test, there was a progressive fall in pain severity on the visual analog scale (VAS) from 63 mm to 31 mm and 22 mm after treatment for 6 and 12 months, respectively ( P < 0.0001). Absence of impairment of function rose from 18% of the patients at the beginning of the study to 69% at 12 months ( P < 0.0001). Sixty-eight patients completed treatment for 2 years; there was a positive response in bone mass in 72.1%, with a rise in lumbar BMD of 9.86% ( P < 0.001). At 24 months, pain severity had fallen from 58 mm at the start of the study to 23 mm ( P < 0.0001) on the VAS. There was no impairment of function in 85% of the patients at 24 months ( P < 0.001). In conclusion, our study confirmed that elcatonin therapy is an effective choice for long-term treatment of patients with osteoporosis.