OBJECTIVE To examine the strength and independence of associations between three major socio-economic indicators (income, education and occupation) and diet quality (DQ) at baseline and after 20-year follow-up. METHODS Cross-sectional and longitudinal analyses using data collected in the Rotterdam Study, a prospective population-based cohort. Participants were categorised according to socio-economic indicators (education, occupation and household income) measured at baseline (1989-1993). Participants aged 55 years or older were included (n=5434). DQ was assessed at baseline (1989-1993) and after 20 years (2009-2011) and quantified using the Dutch Healthy Diet Index, reflecting adherence to the Dutch guidelines for a healthy diet; scores can range from 0 (no adherence) to 80 (optimal adherence). Linear regression models were adjusted for sex, age, smoking status, BMI, physical activity level, total energy intake and mutually adjusted for the other socio-economic indicators. RESULTS At baseline, scores on the Dutch Healthy Diet Index were 2.29 points higher for participants with the highest level of education than for those with the lowest level (95%CI=1.23-3.36); in addition, they were more likely to have a higher DQ at follow-up (β=3.10, 95%CI=0.71-5.50), after adjustment for baseline DQ. In contrast, higher income was associated with lower DQ at follow-up (β=-1.92, 95%CI=-3.67, -0.17), whereas occupational status was not associated with DQ at baseline or at follow-up. CONCLUSIONS In our cohort of Dutch participants, a high level of education was the most pronounced socio-economic indicator of high DQ at baseline and at follow-up. Our results highlight that different socio-economic indicators influence DQ in different ways.