Background and Objective: Stroke at a young age is a societal challenge with a rising incidence. Our aim was to investigate sex differences in risk factors, etiology, and diagnostic process of ischemic stroke in Chinese young adults. Methods: We retro-spectively recruited 411 consecutive patients with first-ever ischemic stroke who were 18 to 50 years of age (mean age, 38.2 +/- 8.1 years, women 31.4%), admitted to Peking Union Medical College Hospital from 2007 to 2018. Sex differences in demo-graphics, risk factors, etiology, and diagnostic testing were analyzed. Results: Females were significantly younger than males (36.9 versus 38.7 years, P<0.05). Hypertension (43.0%), smoking (41.1%), hyperlipidemia (37.2%), and hyperhomocysteinemia (27.9%) were common risk factors, statistically higher among males than females (P<0.05). Stroke etiology showed a significant sex differ-ence that large-artery atherosclerosis and small-vessel diseases were more common among males than females (48.6% versus 19.4%, P<0.001; 9.9% versus 3.1%, P<0.05, respectively). Stroke of other determined etiology was more common among females (50.4% versus 19.1%, P<0.001). Relevant abnormality rates were higher among females on screening for autoimmune diseases and thrombophilia (23.3% versus 11.1%, P<0.05 and 50.0% versus 16.7%, P<0.001, respectively). Conclusions: A high rate of the traditional stroke risk factors and etiological subtype of large artery atherosclerosis in males were found, as well as prominent sex differ-ences in relevant diagnostic testing abnormality rates, providing useful information for developing sex-specific strategies in stroke evaluation and prevention in young adults.