Background: Intravenous (IV) fluid therapy is a ubiquitous intervention in daily clinical practice. However, nationwide detailed hospital- and departmental-level information on IV fluid use is limited. Hence, we aimed to describe the current issuing of isotonic crystalloid solutions across Danish public hospitals. Methods: We conducted a nationwide, retrospective observational study describing the issuing of isotonic crystalloid solutions for IV administration, including 0.9% saline, acetate- and lactate-buffered crystalloid solutions. We assessed fluid issuing at national-, regional-, hospital- and departmental-level from 1 January 2021 to 31 December 2021. We obtained sales figures from the Danish Regional Hospital Pharmacies. Regional characteristics were acquired from the Danish Health Data Authorities online resources. Results are presented graphically and descriptively, including frequencies (%). Results: The total amount of isotonic crystalloid solutions issued across Danish public hospitals in 2021 was 1,487,144 L (67.4% saline, 25.9% acetate- and 6.7% lactate-buffered solutions) equivalent to 2.1 L per hospitalised patient within the study period. Both the issuing of saline versus. buffered crystalloid solutions and the issuing of acetate- versus lactate-buffered solutions varied across geographical regions. Medical departments used saline more frequently (85.3%) than emergency departments (71.5%), surgical departments (70.6%) and anaesthesiological departments including intensive care units (43.0%). Conclusions: In this nationwide observational study, we found that the issuing of different isotonic crystalloid solutions varied based on geographical location. Furthermore, the issuing of different crystalloid solutions differed across departmental settings with medical departments using the highest proportion of saline and anaesthesiological departments using the highest proportion of buffered crystalloid solutions. Editorial Comment: IV fluid administration practices can be assessed across specialties by examining hospital purchasing. This study analysed the use of IV isotonic crystalloid solutions across all major departments of Danish public hospitals for 1 year. Isotonic sodium chloride was the most commonly used fluid in emergency medicine (71%), internal medicine (85%) and surgical departments (71%). Only anaesthesia and intensive care medicine departments used more buffered crystalloid solutions (57%) than isotonic natrium chloride.