Fluid management is an essential competency for hospital doctors, but previous studies suggest junior clinicians lack the necessary 'knowledge' and 'prescription skills' to complete this task, resulting in preventable morbidity and mortality. In this study, preregistration (n=146), core (n=66) and specialty (n=133) medical trainees and general medical consultants (n=11) completed a structured questionnaire exploring fluid management training, confidence, serious adverse event experience and a 20-item fluid management 'knowledge' test. Results were compared with those of intensive care consultants (n=20). Most clinicians reported limited training and extensive 'unreported' serious adverse events experience. Knowledge about fluid and electrolyte requirements, fluid composition and chloride toxicity had improved compared to historical reports but overall test scores (median (interquartile range (IQR)): with a maximum score of 20) were low. Foundation year trainees scored 7 (IQR 5-8), core medical trainees scored 9 (IQR 6-10), specialist registrars scored 8 (IQR 6-10) and general medical consultants scored 8 (IQR 6-12) compared with the intensive care consultant score of 16 (IQR 14-16). Although weakly correlated, fluid management 'confidence' appeared higher than 'knowledge' tests would justify. These results suggest that physicians' fluid management knowledge is inadequate, including that of senior colleagues, compounded by poor training and failure to learn from serious adverse events.