Background: Several studies have demonstrated the deleterious effects of anticholinergic drugs on the cognitive functions of the elderly. However, their effects on the onset of delirium have produced conflicting results. We assessed the association of the anticholinergic burden of treatment at admission according to 3 anticholinergic scales, the ADS, the modified ADS (mADS) and the Marante Scale on the onset of delirium in elderly hospitalized patients. We also analyzed the inter-rater reliability of the scales and their prognostic value in terms of length of stay and hospital mortality.Methods: This retrospective study included patients over 75 years of age hospitalized in medical and surgical departments between January 2014 and June 2019. Delirium was diagnosed by the Confusion Assessment Method (CAM). The anticholinergic burden was assessed by ADS, mADS and Marante Scale in patients with and without delirium.Results were reported as percentages for categorical variables and mean ± standard deviation (SD) and median [interquartile range] for continuous variables after Kolmogorov- Smirnov distribution test. Descriptive statistics were performed using paired Student t-test or Chi-square test. Spearman’s correlation was run to assess the inter-rater reliability between ADS, mADS and the Marante Scale. Results: Among the 1487 patients included, 26% developed delirium. No statistically significant difference in anticholinergic burden was observed between the delirium group and the control group, regardless of the anticholinergic scale used. The correlation coefficient was respectively 0.35 and 0.33 between ADS, mADS and the Marante Scale, and 0.97 between ADS and mADS (all p<0.001). None of the three scales were associated with length of stay, intra-hospital mortality, or one-year mortality. In multivariate analysis, ADS and mADS scores were independently associated with depression (p=0.003 and <0.0001), drug withdrawal (both p<0.001) and the number of drugs on admission (both p<0.001), and Marante Scale score was independently associated with living in a nursing home (p=0.018) and the number of drugs on admission (p<0.0001).Conclusions: Regardless of the scale used, we did not demonstrate a significant association between the anticholinergic burden of treatment upon admission and the onset of delirium during hospitalization.