BACKGROUND: Duchenne muscular dystrophy (DMD) is a hereditary neuromuscular disorder characterized by severe, progressive muscle wasting. Viltolarsen, a formulation consisting of exon 53-skipping antisense oligonucleotides of the dystrophin gene, has been indicated for some patients with DMD. However, reports describing the efficacy and safety of viltolarsen treatment in patients with DMD, particularly those comparing patients receiving viltolarsen with age- and time-period-matched controls, are limited. This study aimed to confirm the safety and efficacy of viltolarsen treatment in patients with DMD. METHODS: We retrospectively reviewed real-world data of patients with DMD aged 6-19 years who started viltolarsen treatment between July 2020 and February 2021 and compared them with age- and time-period-matched patients with DMD who did not receive viltolarsen. RESULTS: Five patients received viltolarsen treatment for over 3 years. Three of the four patients who received viltolarsen once weekly maintained motor function, while one ambulatory patient showed remarkably slow motor function decline. Conversely, eight of nine patients who did not receive viltolarsen and one patient who underwent intermittent viltolarsen treatment showed motor function deterioration. Two patients showed significant treatment-related adverse events, namely swelling of the dorsal surface of the right hand due to extravasation of viltolarsen in one patient and axillary lymph node enlargement due to frequent intravenous infusion in another patient. None of the patients discontinued viltolarsen. CONCLUSIONS: Viltolarsen was a safe and effective treatment for patients with DMD, and the findings highlighted the importance of once-weekly and uninterrupted viltolarsen treatment. The distinct safety and efficacy of viltolarsen require further investigation using a large number of cases and a long follow-up period.