Dry weight assessment (DWA) is essential to efficient therapy of haemodialysis (HD) patients. However, so far objective methods for DWA have not been applicable to daily routine. Thus, exact fluid management in HD remains difficult and is often based on clinical criteria. The aims of this study were (1) to objectively define pre- and post-dialytic ranges of extracellular volume in a large cohort of HD patients (in whom DWA had been defined according to clinical criteria), (2) to compare the hydration status between diabetic and non-diabetic patients, and (3) to assess a patient subgroup that might benefit from correction of target weight.