Background and Purpose— There is little evidence about characteristics of ischemic stroke (IS) occurring in adults with sickle-cell disease (SCD). The objective of this study was to assess characteristics of first-ever IS in adults with SCD and to assess whether they differ from those occurring in child patients with SCD. Methods— Adult and child individuals with SCD who had a first-ever IS were identified from cohorts of patients followed up in an adult and a child sickle cell referral center. Mechanisms of IS were determined by consensus meeting from all available explorations using the following predefined classification: Vasculopathy, cardioembolism, other defined cause, and undetermined. Treatment and stroke recurrences were recorded from prospective follow-up performed in the referral centers. Results— Twenty-nine adults and 26 children had a first-ever IS; mean age (SD) was 7.1 (4.3) and 32.3 (11.6), respectively. With regard to IS mechanism, vasculopathy was less often the cause of IS in adults (12/29, 41%) than in children (24/26, 92%; P <0.001). Other causes of IS in adults were cardioembolism in 7, antiphospholipid syndrome in 1, toxic (cocaine) in 1, and undetermined in 8. Adults with SCD had a higher risk of recurrent stroke (23.1% [7.0–39.2] at 5 years) compared with children (1 recurrence only; P log rank=0.046) despite exchange-blood transfusion in patients with vasculopathy. Conclusions— First-ever IS occurring in adults with SCD has specificities that justify further studies conducted in adults with SCD to improve understanding and management.