In this issue of JAMA Neurology, McKay and colleagues1 found that adults with pediatric-onset multiple sclerosis (POMS) vs those with adult-onset MS (AOMS) performed more slowly on a widely used cognitive screening measure that tests information-processing speed. Patients were drawn from a Swedish nationwide cohort of 5704 adults with definite MS, of whom 300 had POMS. The Symbol Digit Modalities Test (SDMT) was serially administered during neurology visits. Early in their course, those with POMS performed somewhat better than those with AOMS. However, the 2 groups diverged by the time the POMS patients reached 30 years of age, with slower performance in the POMS group relative to the AOMS group, a difference that persisted over time. Although patients with POMS had greater disease duration, the findings remained even when disease duration was adjusted for in the model.