Hydrotherapy is often used in the treatment of fibromyalgia syndrome (FMS), however there has been limited evaluation of its effectiveness. The aim of this systematic review was therefore to examine the effectiveness of hydrotherapy in the management of FMS. AMED, BNI, CINAHL, The Cochrane Library, EMBASE, MEDLINE, ProQuest, PubMed, Science Direct and Web of Science were searched (1990-July 2006). Key words used 'fibromyalgia' and 'hydrotherapy', 'balneotherapy', 'aqua therapy', 'pool therapy', 'water therapy', 'swimming', 'hydrogalvanic', 'spa therapy', 'physiotherapy', 'physical therapy' and 'rehabilitation'. Searches were supplemented with hand searches of selected journals. Randomised controlled trials (RCTs) were assessed for methodological quality using the van Tulder scale. Ten RCTs met the inclusion criteria. Mean methodological quality was 4.5/9 on the van Tulder scale. Positive outcomes were reported for pain, health-status and tender point count. There is strong evidence for the use of hydrotherapy in the management of FMS.