Background: The usual daily weight fluctuations of well-hydrated older hospitalised people have not been documented internationally. To date, dehydration assessments based on a short-term body weight change defined as >2% have been drawn from healthy population data. The present pilot study aimed to describe usual body weight fluctuation at the same time of day over a 3-day time frame in well-hydrated older hospitalised adults. Methods: An observational study of non-acute inpatients (n = 10) admitted to a Geriatric and Rehabilitation Unit, aged 60 years, assessed as wellhydrated, mobile, non-amputee and without conditions that influenced fluid status, was conducted. Participants were weighed hourly over a 9-h period for 3 days. Food and fluid intake, clothing items added or removed, and urine and faecal output were recorded. Results: Weight fluctuation for each participant [mean (SD) 80.2 (4.2) years; male 60.0%, n = 10] over 3 days ranged from 1.1% to 3.6%. Over 3 days, 40.0% (4/10) of participants had weight fluctuations of >2% and 20% (2/10) had weight fluctuations of >3%. Time of weigh-in accounted for 99.8% of the variation in weight fluctuation (P < 0.05), with the lowest fluctuations observed when weights were compared at the same time each day ( 0.4 kg). Conclusions: Weights recorded at the same time daily had the greatest accuracy. Given that the range 1.1-3.6% was within normal weight fluctuations for well-hydrated older hospitalised participants, the weight change indicative of dehydration remains to be established in this setting but appears greater than conventionally used figures.