Title: Inter-Tester Reliability and Agreement of the Cumulated Ambulation Score in Stroke patients: The InTRO-CAS-stroke study Objective: To examine the inter-tester reliability of the total Cumulated Ambulation Score (CAS) and the three activities of the CAS, and to define limits for the smallest change in basic mobility that indicates a real change in patients with stroke. Methods: An intertester reliability study. Setting: Participants: 60 participants from a specialized stroke unit with a mean age of 69.10 ± 13.23 years. The CAS describes a patient's independency in three activities – (1) getting in and out of bed, (2) sit to stand from a chair, and (3) walking ability and was assessed by two independent physiotherapists at median day 3 poststroke. Each activity was assessed on a three-point ordinal scale from 0 (not able to) to 2 (independent). The cumulated score for each activity provides a total CAS from 0 to 6, with 6 indicating independent basic mobility. Relative and absolute reliability was evaluated using weighted kappa, the standard error of measurement (SEM) and minimal detectable change (MDC). Results: The weighted kappa for the total CAS score was 0.816 and ranged from 0.733 to 0.904 for the 3 CAS activities. The SEM and the MDC of the total CAS was 0.37 and 1.03 respectively. Conclusions: The intertester reliability of the CAS is almost perfect, and a change of 1 CAS point for the total CAS indicates a real change in basic mobility, at group level and for an individual patient with stroke Clinicaltrials.gov identifier: NCT05601089