Background: Spa therapies are applied in varying durations. Today, the duration of spa therapy may be long for people with active lives. How should we determine the duration of treatment in order to minimize therapy costs and loss of labor force? Does the duration of treatment have an impact on pain, functional status, and quality of life of patients? Objective: Our aim was to investigate the role of application time on the efficacy of spa therapy in individuals undergoing the same treatment protocol. Methods: This was a randomized, controlled, single-blind clinical trial design. Sixty individuals were divided into two groups: 3 weeks of therapy (group 1) and 2 weeks of therapy (group 2). Pretreatment, posttreatment, and 30-day posttreatment findings were recorded using a visual analog scale (VAS), the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and the Nottingham Health Profile (NHP). Results: The measurements revealed significant improvement after treatment compared to those observed prior to the treatment in both groups, except for the social isolation subgroup. When the groups were compared to each other, significant improvement was observed in pain (VAS, WOMAC, NHP) in favor of group 1 at all measurement times. Conclusion: Our results suggest that spa therapy has positive effects on pain, physical activity, and quality of life in patients, and 15 sessions of therapy had even better effects on pain. We believe that the duration of therapy should be determined considering the efficacy of the therapy on pain as well as the functional situation and quality of life of patients regarding therapy costs.