The body composition monitor (BCM) is a bioimpedance spectroscopy device, specifically developed for patients on hemodialysis (HD) to improve ultrafiltration (UF) programming, based on an objective assessment of the degree of overhydration (OH) at the start of HD. However, its acceptance in clinical practice remains limited because of concerns about the accuracy at the individual level. The aim of this study is to examine the performance of the BCM and to identify means of improvement.