Fluid management is recognized as a basic component of management of patients on dialysis. Fluid overload is an important adverse factor in patient outcomes, and the negative effects of fluid depletion, including on residual renal function, are aIso increasingly being recognized. The complexities of fluid distribution in renal failure need to be understood to inform assessment of hydration. Clinical assessment of hydration is insensitive to abnormalities in hydration. BIA is the most promising technique for objective assessment of fluid status, but it is essential that the underlying principles and limitations are understood, and that results from BIA are utilized in conjunction with clinical assessment rather than in isolation.