Osteoarthritis (OA) is the most common form of arthritis and its current treatment includes non-pharmacological and pharmacological modalities. Spa therapy represents a popular treatment for many rheumatic diseases. The aim of this review was to summarize the currently available information on clinical effects and mechanisms of action of spa therapy in OA of the hand. We conducted a search of the literature to extract articles describing randomized clinical trials (RCTs) in hand OA published in the period 1952–2015. We identified three assessable articles reporting RCTs on spa therapy in hand OA. Data from these clinical trials support a beneficial effect of spa therapy on pain, function and quality of life in hand OA. Spa therapy seems to have a role in the treatment of hand OA. However, additional RCTs are necessary to clarify the mechanisms of action and the effects of the application of thermal treatments.