Objective. The impact of diet quality and physical activity (PA) on weight might be different according to socioeconomic status. Our aim was to estimate associations between adherence to nutritional guidelines and BMI and the interaction with socioeconomic characteristics. Methods. A total of 11,931 men and 39,737 women from the NutriNet-Sante cohort (France, 2009-2012) were included in this cross-sectional analysis. The association between PNNS-GS (a score estimating adherence to French nutritional guidelines) and BMI was assessed by multivariate linear regression. A modified score (mPNNS-GS) separating diet quality from PA was also used. Results. BMI, overweight and obesity displayed an inverse gradient from less to more educated groups, whereas PNNS-GS increased. A higher PNNS-GS was associated with a lower BMI, more importantly in the less educated: BMI decrease ranged from -1.1% in less educated to -0.7% in more educated men and from -0.6% to -0.3% in women. The effect of mPNNS-GS and PA in particular was also stronger among less educated subjects. Conclusion. Overall, better adherence to nutritional recommendations was inversely associated with BMI, and this association was stronger in the less educated groups. This suggests that nutritional policies should still concentrate on promoting access to a healthier diet and PA, especially among less educated individuals. (C) 2013 Elsevier Inc. All rights reserved.