Background: Many investigations into the determinants of hand hygiene (HH) behaviour have explored only individual predictors or were designed according to arguably overly simplistic models of behaviour. Consequently, important influences on HH behaviour, including habit and emotion, are sometimes neglected. This study is the first to employ the Theory of Interpersonal Behaviour as a comprehensive model for understanding the determinants of HH behaviour. Method: A self-report questionnaire was conducted with staff from two large UK veterinary referral practices. Participants ( n = 75) reported their HH behaviour and responded to statements rating the importance of social norms, self-protection, patient protection, time pressures, access to equipment, habit and disgust, to their HH behaviour. Results: Regression analysis showed that, overall, determinants explained 46% of variance ( p < .001) in self-reported HH behaviour, with time constraints being the strongest predictor ( β = −.47, p < .001) followed by difficulty finding equipment ( β = −.21, p = .05). Discussion: Time constraints may be the most important influence on HH adherence among the determinants investigated. Future researchers should consider employing theoretical models to aid a more comprehensive understanding of the psychology underlying HH adherence and HH interventions.