Bathing in water (balneotherapy or spa therapy) has been frequently and widely used in classical medicine as a cure for diseases. This paper reviews the present literature on the use of balneotherapy in dermatologic, chronic musculoskeletal (inflammatory and non-inflammatory), metabolic and psychological conditions.We performed a systematic review on related papers appearing in the Medline and Cochrane Library database from 1966 to 2003 that included randomized controlled and non-randomized clinical trials using balneotherapy. We also determined to reflect where possible the chemical compositions of spas.The major dermatologic and musculoskeletal diseases that are frequently treated by balneotherapy with a remarkable rate of success are atopic dermatitis, psoriasis, rheumatoid arthritis (RA), ankylosing spondylitis, osteoarthritis and low back pain. Moreover, the effects of spa therapy on several metabolic conditions are discussed. The mechanisms by which broad spectrums of diseases respond to spa therapy probably incorporate chemical, thermal and mechanical effects.The importance of balneotherapy either alone or as complement to other therapies should be considered after, or accompanying, orthodox medical treatments.