Background Associated with both socioeconomic position and health outcomes, health literacy (HL) may be a mechanism contributing to social disparities. However, it is often difficult for general practitioners (GPs) to assess their patients’ HL level. Objective To analyse disagreements about patient HL between GPs and their patients according to the patient’s socioeconomic position. Methods For each of the 15 participating GPs (from the Paris-Saclay University network), every adult consulting at the practice on a single day was recruited. Patients completed the European HL Survey questionnaire and provided socio-demographic information. For each patient, doctors answered 4 questions from the HL questionnaire with their opinion of the patient’s HL. The doctor–patient disagreement about each patient’s HL was analysed with mixed logistic models to study its associations with patients’ occupational, educational, and financial characteristics. Results The analysis covered the 292 patients (88.2% of the 331 included patients) for whom both patients and GPs responded. The overall disagreement was 23.9%. In all, 71.8% of patients estimated their own HL as higher than their doctors did, and the gap between doctors’ answers and those of their patients widened from the top to the bottom of the social ladder. The odd ratio for the ‘synthetic disagreement’ variable for workers versus managers was 3.48 (95% CI: 1.46–8.26). Conclusions The lower the patient’s place on the social ladder, the greater the gap between the patient’s and doctor’s opinion of the patient’s HL. This greater gap may contribute to the reproduction or maintenance of social disparities in care and health.