Purpose: This multicenter study examined the effectiveness and tolerability of lacosamide (LCM) for children and young adults with epilepsy, particularly in patients who had previously been treated with other sodium channel blockers (SCBs) and the difference in effectiveness and tolerability when using other concomitant SCBs. Methods: We retrospectively studied the clinical information of patients aged <30 years given LCM to treat epilepsy. The effectiveness and adverse events (AEs) of LCM and the other SCBs were investigated. Factors related to the effectiveness and AEs of LCM, such as the number of antiepileptic drugs (AEDs) tried before LCM and concomitantly used SCBs, were also studied. Results: We enrolled 112 patients (median age = 11 years). One year after starting LCM, 29% of the patients were seizure free, and 50% had a ≥50% seizure reduction. Of the patients, 17% experienced AEs, the most common being somnolence. A ≥50% seizure reduction was observed for LCM in 30% of patients in whom other SCBs had not been effective. Lacosamide produced a ≥50% seizure reduction in 35% of the patients taking one concomitant SCB. By contrast, no patients had ≥50% seizure reduction, and 33% developed AEs, when LCM was administered concomitantly with two SCBs. Conclusions: Lacosamide was effective in 30% of children and young adults in whom other SCBs had not been effective. The effectiveness of LCM may differ from that of other SCBs, and it is worth trying in patients with epilepsy resistant to other AEDs.