Background: Several diagnostic imaging criteria are being described and examined in pediatric multiple sclerosis (MS). Compared to adults, children are more likely to experience acute or relapsing demyelinating episodes of various etiologies which show similar clinical and magnetic resonance imaging (MRI) findings. Aim: To investigate the fulfillment of MRI diagnostic criteria at initial episode in pediatric MS. Methods: We reviewed our series of children and adolescents with the final diagnosis of clinically definite MS and applied the McDonald dissemination in space (DIS) and KIDMUS criteria to their initial MRI scans. Results: Thirty patients (17 girls, 13 boys), most with brainstem dysfunction and polysymptomatic presentation, were included in the study. Twenty-five (83.3%) patients fulfilled both McDonald and KIDMUS criteria. Patients who did not meet any McDonald DIS criteria did not meet KIDMUS criteria either. Only one patient met the McDonald criteria but not the KIDMUS criteria because of the absence of lesions perpendicular to corpus callosum. Conclusions: Our results show 5/30 (16.6%) of MS patients may not present the diagnostic MRI features initially. The variable sensitivity observed for the current MRI criteria in different series can be due to referral biases, differences between populations and length of follow-up, and the definition of MS patients by two attacks only. (C) 2009 Elsevier B.V. All rights reserved.