The aim of this study was to evaluate both the short-term and the long-term effectiveness of spa therapy in patients with primary hand osteoarthritis (OA). This was a prospective randomized, single blind controlled trial. Sixty outpatients with primary bilateral hand OA were included in the study and randomized to one of two groups. One group (n = 30) was treated with 12 daily local mud packs and generalized thermal baths with a sulfate-calcium-magnesium-fluorides mineral water added to usual treatment. The control group (n = 30) continued regular outpatient care routine (exercise, NSAIDs and/or analgesics). Each patient was examined at baseline, after 2 weeks, and after 3, 6, 9 and 12 months. Primary outcome measures were global spontaneous hand pain on a visual analogue scale (VAS) and the functional index for hand osteoarthritis (FIHOA) score; secondary outcomes were health assessment questionnaire (HAQ), duration of morning stiffness, medical outcomes study 36-item short form (SF-36) and symptomatic drugs consumption. Our results demonstrated that the efficacy of spa therapy was significant in all the assessed parameters, both at the end of therapy and after 3 months; the values of FIHOA, HAQ and drugs consumption continued to be significantly better after 6 months in comparison with baseline. There were no significant modifications of the parameters throughout the follow-up in the control group. Differences between the two groups were significant for all parameters at the 15th day and at 3 months follow-up; regarding FIHOA, HAQ, and symptomatic drugs consumption, the difference between the two groups persisted and was significant at 6month follow-up. Tolerability of spa therapy seemed to be good. In conclusion, our results confirm that the beneficial effects of spa therapy in patients with hand OA last over time.