This retrospective study is based on the Helsinki Young Stroke Registry data. The registry includes all consecutive 15-to 49-year-old Background and Purpose-Poststroke infections (PSIs) worsen the outcome in acute ischemic stroke, but the effect of preceding infection (PI) is controversial. Data on young patients are scarce. We characterized PI and PSI in young adults with first-ever stroke and studied whether they are associated with 3-month and long-term outcomes, recurrent vascular events, and death. Methods-From our database of 1008 consecutive patients aged 15 to 49 years, we included in the present study those who had brain imaging done within the first 2 days from stroke onset. Outcomes were unfavorable at 3 months and during long-term follow-up, vascular events, and all-cause death. Logistic regression and Cox proportional models were used to determine associations between infections and clinical outcomes. Results-A total of 681 patients (62.3% men) fulfilled the inclusion criteria. Of these, 70 (10.3%) had PI, most commonly upper respiratory tract infection, and 103 (15.1%) had PSI, most commonly pneumonia. After adjusting for sex, age, and risk factors, both PI (odds ratio, 2.86; 95% confidence interval, 1.48-5.54) and PSI (odds ratio, 2.26; 95% confidence interval, 1.08-4.76) were independently associated with unfavorable 3-month outcome. PSI was also associated with long-term (follow-up, 7.8±4.0 years) higher risk of all-cause death. Conclusions-In young patients with ischemic stroke, both PI and PSIs are associated with unfavorable short-term outcome.PSIs are also associated with higher long-term mortality. (Stroke. 2013;44:3331-3337.)