Objectives: This study aims to determine the inter- and intraobserver reliabilities of an aetiological classification devised as part of a community-based stroke register. Methods: Patients with first-ever acute ischaemic stroke were clinically assessed and received investigation according to a set protocol. Results of the clinical assessment and investigations were used to determine an aetiological stroke subtype for each patient by observer 1. Aetiological subtypes consisted of extracranial large artery atherosclerosis (LAAec), intracranial large artery atherosclerosis (LAAic), high-risk cardioembolism (CH), medium-risk cardioembolism (CM), small vessel occlusion (SVO), other aetiology (OTH), no aetiology identified (NA) and multiple probable or multiple possible aetiology (MPA). The same data were distributed to a further four observers along with the criteria for the classification system. Two of the observers were …