Few controlled trials of disease-modifying therapies (DMTs) have been conducted on the pediatric-onset multiple sclerosis (PoMS) population, leading to extensive off-label use of therapies approved only for adults. This highlights the need for real-world evidence to guide clinical practice. Clinical registries can offer high-quality data, but limitations such as missing and erroneous information must be considered. This validation study compared Swedish Multiple Sclerosis registry data from 122 PoMS patients to medical records. Generally (≥89%), data were confirmed. However, missing data exceeded 30% for rituximab infusions, magnetic resonance imaging, and relapses. Overall, the registry provides valid, real-world data on DMT use in PoMS.