We report our observations in 427 stroke patients (305 Saudis, 122 non-Saudis with an age range of 14 months to 85 years) seen in a tertiary hospital in the eastern province of Saudi Arabia over an 8-year period. Of these patients, 115 (27%) were between 18 and 45 years old, and constituted the "young stroke patients" for this study. The hospital frequency for the young was 5/10,000 inpatients. In general, there was a male preponderance, with a male:female ratio of 2.2:1 and 7:1 for Saudis and non-Saudis, respectively. Ischemic stroke (55%) was more frequent than hemorrhagic stroke (25%), and the stroke was unspecified in 20%. The main etiologic factors were hypertension, diabetes mellitus and cardiac disorders. In the young population, the frequencies of hemorrhagic and ischemic strokes were similar. In this group, the main causes of intracerebral hemorrhage were aneurysms and arteriovenous malformations, while arteriosclerosis and embolism of cardiac origin were responsible for the ischemic strokes. In Saudis, the stroke types were 59% ischemic, and 17% hemorrhagic, as against 45 and 48% in non-Saudis, respectively. Most ischemic strokes were found in Saudis (78%). Intracerebral hemorrhage accounted for 63% of all hemorrhagic strokes, and was more frequent in Saudis but subarachnoid hemorrhage was three times more common in non-Saudis. In the young stroke patients, interethnic comparison showed that individuals from the Far East were nine times more likely to have hemorrhagic than ischemic stroke compared to the others (odd's ratio = 8.7), and the etiology of ischemic stroke remained undetermined in 67% of those from the Indian subcontinent.(ABSTRACT TRUNCATED AT 250 WORDS)