Résumé : Background: An increasing number of patients older than 80 years are undergoing anesthesia, but little information is available regarding pharmacodynamic effects of myorelaxants in this population. This study aims to compare the time course of rocuronium neuromuscular block in patients ≥ 80 years with those of younger adults. Methods: Under total intravenous anesthesia with propofol and sufentanil, time course of a bolus of rocuronium 0.6 mg/kg neuromuscular block was assessed with acceleromyography in patients ≥ 80 and in patients 20–50 years old. Onset time, clinical duration, duration until 90% and 100% recovery of baseline were determined. Results: Data from 32 patients were analyzed, 16 were ≥ 80 years and 16 were 20–50 years old. Demographic data are shown in Table 1. In the group ≥ 80, onset time was 190 s ± 46 s compared to 123 s ± 40 s in the group 20–50, P < 0.001 and the clinical duration was 52 [48–69.5] min and 36 [34–41] min, respectively, P < 0.001. Duration to 90% recovery of baseline was 77.5 [71–88.5] min and duration to 100% recovery of baseline was 91.2 [82.2–98] min in patients ≥ 80 years and the corresponding values in the patients 20–50 years old were 53.5 [49–55.5] min and 59.5 [56.5–70.25] min, respectively, P < 0.001. Conclusion: Compared to younger adults rocuronium shifted in patients ≥ 80 years from a rapid onset, intermediate acting compound to a slower onset, long-acting compound. Trial registration: ClinicalTrials.gov identifier: NCT03551652 (29/05/2018).