We evaluated the efficacy of clodronate for treating active erosive osteoarthritis of the hand and to compare it with hydroxychloroquine. Group A consisted of 24 patients treated for 24 months with clodronate 300 mg i.v. for 7 days, followed by clodronate i.m. 100 mg for 14 days every 3 months. Group B comprised 14 patients treated with hydroxychloroquine 400 mg daily for 30 days, followed by 200 mg daily for the next 11 months. In group A, 21/24 patients completed the trial and obtained significant pain reduction (p < 0.001), Dreiser's score (p = 0.012), and number of tender joints (p = 0.011). Strength of right (p = 0.04) and left (p = 0.016) hands, physician's global assessment (p ≤ 0.001), and patient's global assessment (p = 0.021) improved. In group B, 8/14 patients completed 12 months of the study, which showed the inefficacy of hydroxychloroquine and its lack of acceptance by patients (worsening pain and patient's global assessment). Therefore, enrolment was stopped. Differences between groups showed a pain decreasing trend for group A and a slightly increasing one for group B (p = 0.018). Physician and patient global assessments showed a strong increase in group A compared with group B (p < 0.001). Clodronate is effective in erosive osteoarthritis; hydroxychloroquine seems to be ineffective.