The objective of the study was to assess the efficacy and the safety of pamidronate (APD) in recalcitrant reflex sympathetic dystrophy (RSD). Ten women and 13 men with a mean (+/-standard deviation, SD) age of 44 +/- 11 years were included. The involved sites were: the ankle (n = 10), the foot (n = 7), the hand (n = 3), the hip (n = 2), the knee (n = 2) and the shoulder (n = 1). Some patients had more than one site involved. Mean (+/-SD) duration of the disease was 15 +/- 13 months. RSD was in pseudo-inflammatory phase in 16 patients and in ischaemic phase in 7 patients. RSD was post-traumatic in 17 cases; 11 patients have been previously treated unsuccessfully by sympathetic blockades. APD was administered intravenously (perfusion) to a dose of 1 mg/kg/day during 3, 2 or one day. Fourteen patients received APD during 3 consecutive days whereas 7 patients have been treated during 2 consecutive days and 2 patients only during 1 day mainly due to adverse events. Efficacy was assessed by a decrease of pain = visual analogic scale (VAS, 0-100 mm) and verbal scale (PVS, range 0-3). Moreover, the patient and the observer have estimated the efficacy of the treatment on a verbal scale (EVS, range 0-3). Measurements of these parameters were performed immediately before the treatment and 7, 30, 60 and 90 days later. The maximum duration after treatment was 9 months. A significant decrease of VAS and PVS were observed between D0 and D30 (p = 0.0002 and p = 0.0002 respectively), D0 and D60 (p = 0.0004, p = 0.0004 respectively), and D0 and D90 (p = 0.00003, p = 0.0001 respectively). A significant increase of EVS was only observed between D0 and D90 (p = 0.03). Adverse events were noted in 14 patients: transient fever (n = 6), venous inflammation (n = 2), transient symptomless hypocalcaemia (n = 3), nausea (n = 1), lymphopenia (n = 1), transient hypertension (n = 1). These results suggest an efficacy of APD in recalcitrant RSD. Double-blind placebo controlled studies are required to back up these preliminary results.