['Fluid balance for the surgical patient has been proven very important for the postoperative outcome and development of complications. The aim of this study was to evaluate, for the first time in modern times, the accordance between nurse-based fluid charting (cumulated fluid balance) and body weight change for general surgical patients.', 'This was a descriptive study with prospectively collected data from two clinical randomized multicenter trials. A total of 113 patients from American Society of Anesthesiology group I-III undergoing elective colorectal surgery were included. Cumulated fluid balance and body weight change were charted preoperatively and daily at the same time during a postoperative period of 6 days. Differences were calculated by subtracting cumulated fluid balance from body weight change (1 g = 1 mL), and agreement was assessed by making Bland-Altman plots as well as Pearson correlations.', 'From day 1 to 4, the mean difference between cumulated fluid balance and body weight change was below 0.4 kg/L. On day 5 and 6, the discrepancies increased with mean differences of, respectively, 1.2 kg/L (p < 0.002*) and 2 kg/L (p < 0.0001*). Bland-Altman plots showed increasingly poor agreement for all postoperative days with wide limits of agreement, ranging from more than 6 kg/L to almost 10 kg/L. Pearson correlations were moderate to strong at all times ranging from 0.437 (day 1) to 0.758 (day 4).'] Is clinical Assessment of Fluid Balance Incomplete for Colorectal Surgical Patients?