Background and Objectives: There is a paucity of comparative studies on young strokes between populations of different ethnicities and geographical regions. The purpose of this study was to compare the patterns, risk factors and etiologies of ischaemic stroke in younger patients between stroke registries in Malaysia and Australia. Methods: From January 2007 to March 2008, all consecutive ischaemic stroke patients from the age of 18 to 49 were studied. Results: There were 67 patients for Malaysia and 61 for Australia, with 4 deaths in the Malaysian series (case-fatality of 6%), and no deaths for Australia. The mean age was 41.5±8.8 yrs for Malaysia and 40.1±8.8 years for Australia. The ethnic origin was Malays, Chinese and Indian for Malaysia, and Caucasians (85%) for Australia. The sex ratio was M : F = 1.4 : 1 for Malaysia and 1.54 :1 for Australia. The differences in risk factors for Malaysia versus Australia were: Diabetes (OR 7.25; 95% CI 2.78-19.45), hypertension (OR 6.42; 95% CI 2.75-15.22) and chronic renal disease (OR 5.2; 95% CI 1.02-35.87). Conversely, smoking was a signifi cant risk factor for Australia (OR 2.75; 95% CI 1.2-6.37). The Malaysian patients have signifi cantly higher proportions of large vessel atherosclerosis and small vessel occlusion by TOAST classifi cation, accounting for 60% of patients, while the Australian series had greater proportions of cardioembolism and patients in the determined aetiologies category, specifi cally vascular dissection. Conclusion: There were signifi cantly more large vessel atherosclerosis and small vessel occlusion among young Malaysians with ischaemic stroke as compared to Australia. Neurology Asia 2010; 15(1) : 1 – 9 Address correspondence to: Dr. Kay Sin Tan, Division of Neurology, Dept of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia. E-mail: firstname.lastname@example.org INTRODUCTION Cerebral infarction in young adults is responsible for signifi cant socioeconomic loss worldwide. Many studies based on hospital-based registries have demonstrated a broad spectrum of aetiologies and risk factors. In addition, unique aetiologies have also been identifi ed such as moya-moya syndrome, vascular dissections, haematological causes, vasculitis and drugs in varying proportions. Globally, studies on young adults with cerebral infarctions in developed and developing countries have observed large variations in the heterogeneity of stroke subtypes and classifi cation. Interestingly, strokes of undetermined aetiology varied widely from 5-44% while combined categories of large vessel atherosclerosis and small vessel occlusion showed similar large variation from 3%-42.5%. The cardioembolic category varied from between 12.6% to 54% among studies while the proportions in the undetermined or unknown category ranged from 15% to 42.5%. Many conventional and recognised risk factors in young stroke patients have also been described. Overall, the results showed these variations due to many reasons including geographical location, referral bias, study methodologies, classifi cation schemes and the intensity of investigations. Comparative studies between young adults with cerebral infarction in developed and developing countries involving different ethnic groups and geographical regions were rare. An extensive literature review revealed only one previous study, comparing Thai and Dutch patients. In this study, cardioembolic strokes were more common in Thai patients while atherothrombotic events and traditional risk factors were more signifi cant in the Dutch series. Accordingly, we hypothesized that cerebral infarction in younger adults (under the age of ORIGINAL ARTICLES Neurology Asia April 2010 2 50) in urban Australia would be predominantly from large vessel atherosclerosis and small vessel occlusion due to large proportion of patients with conventional risk factors while the young stroke population from urban Malaysia would reveal a lower proportion of atherothrombotic causes and greater numbers of determined strokes based on TOAST criteria secondary to unique aetiologies, common to Asia. This study was undertaken to examine this hypothesis.