Several studies have shown that an individual’s socioeconomic status influences participation in cancer screening. However, these studies were primarily based on questionnaires and were systematically subject to selection bias. The objective of this study was to analyze the influence of socioeconomic characteristics on participation in an organized colorectal cancer screening program using an unbiased sample of the target population in the Calvados department (n=180,045). Individual participation data and aggregated socioeconomic data, derived respectively from the organization responsible for organized screening and the population census, were analyzed simultaneously using a multilevel model. Women participated more than men (OR=1.33; 95% CI [1.21–1.45]). Participants were older (mean age: 61.2 years) than non-participants (60.5) (p-value < 0.01). Participation decreased with increasing socioeconomic vulnerability; there was a significant difference in the probability of participation between the most affluent and the most vulnerable areas (OR = 0.68; [0.59–0.79]). No significant influence of the density of general practitioners was found. These analyses suggest that screening inequalities could be reduced through targeted interventions focused on populations at risk of low participation, identified both socially and geographically. (R.A.)