Purpose: This study was done to examine the differences in the fluid volume deficit according to levels of depression and BMI. The results of this study will provide fundamental information for developing nursing interventions for hydration management. Method: The participants were 51 hospitalized elderly people in K province. Data were collected from September 4 to 30, in 2006. A structured questionnaire was used for the data collection. Frequencies, Percentages, Means, Standard Deviation, t-test, Mann-Whitney U test, and Kruskal-Wallis test were used with the SPSS Program to analyze the data. Results: There were significant differences in the fluid volume deficit between elders in the depressed and normal groups. Participants who had a BMI of less than $21kg/m^2$ had the highest fluid volume deficit. Conclusion: Water is an essential part of the human body although it is least studied in elderly people. Health care providers need to increase awareness of the importance of hydration status among hospitalized elderly people with chronic illnesses.