Objective: We analyzed the characteristics of patients whose BIS-based DWs were over- and underestimated.In this retrospective cohort study, we evaluated 1,555 patients undergoing maintenance hemodialysis inChungnam National University Hospital. The gap (DW) was calculated by comparing the BIS and clinicalDWs. Methods: We analyzed the clinical characteristics of patients with positive (n = 835) and negative (n = 720)gaps. Compared with other patients, the DW-positive group was taller, had higher extracellular water(ECW) level and extracellular/intracellular water index (E/I); and had lower weight, body mass index (BMI),lean tissue index (LTI), fat tissue index (FTI), fat mass (FAT), and adipose tissue mass (ATM), as well as lowerlevels of hemoglobin, total protein, albumin, and phosphorous. The DW-negative group exhibited higherlevels of hemoglobin, total protein, albumin, and phosphorous, as well as elevated BMI, FTI, FAT, and ATM;however, it had lower height, ECW, and E/I. Linear regression analysis revealed that FAT significantly predictedDW accuracy. Results: The clinical DW of patients with malnutrition and a low fat mass tended to be underestimated,while the clinical DW of patients with comparatively large fat reserves tended to be overestimated. Thesecharacteristics of dialysis patients will aid in the correction of BIS-associated DW errors Conclusions: Objective: Accurate dry weight (DW) estimation is important for hemodialysis patients. Althoughbioimpedance spectroscopy (BIS) is commonly used to measure DW, the BIS-based DW frequently differsfrom the clinical DW.  Methods: We analyzed the characteristics of patients whose BIS-based DWs were over- and underestimated.In this retrospective cohort study, we evaluated 1,555 patients undergoing maintenance hemodialysis inChungnam National University Hospital. The gap (DW) was calculated by comparing the BIS and clinicalDWs. Results: We analyzed the clinical characteristics of patients with positive (n = 835) and negative (n = 720)gaps. Compared with other patients, the DW-positive group was taller, had higher extracellular water(ECW) level and extracellular/intracellular water index (E/I); and had lower weight, body mass index (BMI),lean tissue index (LTI), fat tissue index (FTI), fat mass (FAT), and adipose tissue mass (ATM), as well as lowerlevels of hemoglobin, total protein, albumin, and phosphorous. The DW-negative group exhibited higherlevels of hemoglobin, total protein, albumin, and phosphorous, as well as elevated BMI, FTI, FAT, and ATM;however, it had lower height, ECW, and E/I. Linear regression analysis revealed that FAT significantly predictedDW accuracy. Conclusions: The clinical DW of patients with malnutrition and a low fat mass tended to be underestimated,while the clinical DW of patients with comparatively large fat reserves tended to be overestimated. Thesecharacteristics of dialysis patients will aid in the correction of BIS-associated DW errors