OBJECTIVE: We describe the prevalence and range of incidental intracranial abnormalities identified through MRI of the brain in a large group of children screened for a clinical trial. METHODS: We included 953 children between 5 and 14 years of age who were screened with MRI of the brain for the Silent Infarct Transfusion Trial. All had sickle cell anemia or sickle beta-null thalassemia. MRI scans were interpreted by 3 neuroradiologists. MRI scans reported to have any abnormality were reviewed by 2 study neuroradiologists. Incidental findings were classified into 4 categories, that is, no, routine, urgent, or immediate referral recommended. Cerebral infarctions and vascular lesions were not considered incidental and were excluded. RESULTS: We identified 63 children (6.6% [95% confidence interval: 5.1%-8.4%]) with 68 incidental intracranial MRI findings. Findings were classified as urgent in 6 cases (0.6%), routine in 25 cases (2.6%), and no referral required in 32 cases (3.4%). No children required immediate referral. Two children with urgent findings underwent surgery in the subsequent 6 months. CONCLUSION: In this large cohort of children, incidental intracranial findings were identified for 6.6%, with potentially serious or urgent findings for 0.6%.