STUDY OBJECTIVES: To assess the direct and indirect contributions of material, behavioural, and psychosocial factors to the explanation of educational inequalities in mortality simultaneously. DESIGN: Prospective observational study (1991-1998). SETTING: General population from south east Netherlands. PARTICIPANTS: 3979 men and women aged 15-74 years without severe chronic disease at baseline (1991). MAIN RESULTS: Material factors (type of health insurance, financial problems, and housing tenure), psychosocial factors (life events and external locus of control), and behavioural factors (smoking habits and physical activity) together reduced the relative risk of mortality of the lowest educated group from 2.57 (95%CI 1.43 to 4.64) to 1.01 (95%CI 0.50 to 2.03). Of these three groups of factors, material factors contributed most to the educational inequalities. Part of the contribution of material factors was via psychosocial factors and part via behavioural factors. Psychosocial factors contributed to educational inequalities, partly via behavioural factors. Behavioural and psychosocial factors contributed only marginally to the explanation independent of material factors. CONCLUSION: Educational inequalities in mortality were explained by material, psychosocial, and behavioural factors. Material factors contributed most to the explanation, partly via psychosocial and behavioural factors. Improving the material situation of lower educated people may substantially reduce educational inequalities in mortality, partly via the psychosocial and behavioural consequences of improved material circumstances.