Most hemodialysis (HD) patients are able to finish dialysis at or below the normally hydrated weight determined using the body composition monitor (BCM). However, a minority become symptomatic when they are still fluid overloaded based on BCM-measured overhydration (OH). Malnourished patients frequently fall into this group, suggesting that they may have OH that is inaccessible to ultrafiltration. To isolate any effect of malnutrition on BCM-measured OH from those relating to renal failure, OH measurements for 20 elderly subjects with normal renal function who were classified as malnourished were compared with an age-matched cohort with no known nutritional issues. Body composition monitor measurements were also made on five malnourished HD patients. Mean OH for malnourished subjects with normal renal function was not significantly different from an age-matched cohort without known nutritional deficiencies (1.3 and 1.1 L, respectively; p = 0.5). Post-dialysis OH for HD patients ranged from −0.1 to +4.5 L. A slightly elevated BCM-measured OH appears to be common in elderly subjects and may be explained by changes in the composition of adipose tissue. The effect of malnutrition could not be isolated from sarcopenia, but this study supports the need for caution when reducing target weight in vulnerable patients.