MRI plays a pivotal role in the diagnosis of multiple sclerosis (MS) in children, as it does in adults. The presence of multiple lesions in CNS locations commonly affected by MS, along with the presence of both enhancing and nonenhancing lesions, can facilitate a diagnosis of MS at the time of a first attack, whereas the accrual of serial lesions or new clinical attacks over time confirms the diagnosis in patients not meeting such criteria at onset. T2 and enhancing lesion accrual could serve as a primary outcome metric for pediatric MS clinical trials of selected therapies with anti-inflammatory activity in order to facilitate feasible trial size numbers. More-advanced MRI techniques reveal the impact of MS on tissue integrity within both T2-bright and T1-hypointense lesions and regions of normal-appearing tissue. Volumetric MRI analyses quantify the impact of MS on age-expected brain growth, and fMRI reveals activation and resting-state functional connectivity patterns in patients with pediatric MS that differ from those seen in healthy age-matched youth. Such studies are of critical importance because MS onset during childhood may profoundly influence maturing and actively myelinating neural networks. High-field MRI visualizes MS pathology at a near-microscopic level and has the potential to more fully explain mechanisms for cognitive impairment, fatigue, and disability in patients with pediatric MS.