Background: The cognitive behavioural (CB) model of health anxiety proposes parental illness leads to elevated health anxiety in offspring by promoting the acquisition of specific health beliefs (e.g. overestimation of the likelihood of illness). Aims: Our study tested this central tenet of the CB model. Method: Participants were 444 emerging adults (18–25-yearsold) who completed online measures and were categorized into those with healthy parents (n = 328) or seriously ill parents (n = 116). Results: Small (d = .21), but significant, elevations in health anxiety, and small to medium (d = .40) elevations in beliefs about the likelihood of illness were found among those with ill vs. healthy parents. Mediation analyses indicated the relationship between parental illness and health anxiety was mediated by beliefs regarding the likelihood of future illness. Conclusions: Our study incrementally advances knowledge by testing and supporting a central proposition of the CB model. The findings add further specificity to the CB model by highlighting the importance of a specific health belief as a central contributor to health anxiety among offspring with a history of serious parental illness.