Fluid resuscitation is a widely-used treatment in acute and emergency medicine, however, the process used to perform a fluid assessment has never been studied. This qualitative study explored how acute physicians describe their approach to assessing for fluid resuscitation. 18 clinicians of varying grades consented to a semi-structured interview. Transcripts were coded and analysed using thematic analysis. Participants described three subtypes of assessment; screening assessment, emergency assessment and formal assessment. Whether a patient was ‘sick’ was key to determining which assessment they would receive. Marked heterogeneity was noted in the assessment processes, particularly regarding the use of history-taking. Further research is required to determine how the information gathered in these assessments is used to decide when fluid resuscitation is indicated.