Ischaemic stroke (IS) in young adults has been increasingly recognized as a serious health condition. Stroke aetiology is different in young adults than in the older population. This study aimed to investigate aetiology and risk factors, and to search for predictors of outcome and recurrence in young IS patients. We conducted a prospective multicentre study of consecutive IS patients aged 16-55 years. Baseline demographic data, risk factors, stroke aetiology including systematic genetic screening for Fabry disease and severity were assessed and related to functional neurological outcome (modified Rankin Scale, mRS), case fatality, employment status, place of residence, and recurrent cerebrovascular events at 3 months. In 624 IS patients (60% men), median age was 46 (IQR 39-51) years and median NIHSS on admission 3 (IQR 1-8). Modifiable vascular risk factors were found in 73%. Stroke aetiology was mostly cardioembolism (32%) and of other defined origin (24%), including cervicocerebral artery dissection (17%). Fabry disease was diagnosed in 2 patients (0.3%). Aetiology remained unknown in 20%. Outcome at 3 months was favourable (mRS 0-1) in 61% and fatal in 2.9%. Stroke severity (p < 0.001) and diabetes mellitus (p = 0.023) predicted unfavourable outcome. Stroke recurrence rate at 3 months was 2.7%. Previous stroke or TIA predicted recurrent cerebrovascular events (p = 0.012). In conclusion, most young adults with IS had modifiable vascular risk factors, emphasizing the importance of prevention strategies. Outcome was unfavourable in more than a third of patients and was associated with initial stroke severity and diabetes mellitus. Previous cerebrovascular events predicted recurrent ones.