BACKGROUND AND OBJECTIVES: The study reported here investigated the causal relationships in the health impairment process of employee well-being, and the mediating role of burnout in the relationship between work overload and psychological ill-health symptoms, over time. The research is deemed important due to the need for longitudinal evidence of the health impairment process of employee well-being over three waves of data. DESIGN: A quantitative survey design was followed. Participants constituted a longitudinal sample of 370 participants, at three time points, after attrition. METHODS: Descriptive statistics and structural equation modeling methods were implemented. RESULTS: Work overload at time one predicted burnout at time two, and burnout at time two predicted psychological ill-health symptoms at time three. Indirect effects were found between work overload time one and psychological ill-health symptoms time three via burnout time two, and also between burnout time one and psychological ill-health symptoms time three, via burnout time two. CONCLUSIONS: The results provided supportive evidence for an "indirect-only" mediation effect, for burnout's causal mediation mechanism in the health impairment process between work overload and psychological ill-health symptoms.