Eteplirsen (Exondys 51) is an antisense oligonucleotide designed to induce exon 51 skipping that is developed by Sarepta Therapeutics. Intravenous eteplirsen has received accelerated approval from the US FDA for the treatment of Duchenne muscular dystrophy (DMD) in patients with a confirmed mutation of the DMD gene amenable to exon 51 skipping. Eteplirsen has orphan drug designation in the USA and EU, and rare paediatric disease designation in the USA for use in DMD. In the phase III PROMOVI trial, eteplirsen significantly increased dystrophin levels from baseline in muscle tissues of 12 evaluable patients with DMD after 48 weeks of treatment. This finding is supported by data from phase II trials. Long-term treatment with eteplirsen was associated with a decrease in the rate of decline in ambulation and pulmonary function in an open-label extension of a phase II trial. Eteplirsen was generally well tolerated in clinical trials. This article summarizes the milestones in the development of eteplirsen leading to this first approval for DMD.