Fomivirsent was approved by the FDA in 1998 and by the EMA in 1999 as the very first antisense drug used to treat CMV retinitis in patients with AIDS. To date, it has been the only first generation antisense oligonucleotide used in therapy. Fomivirsen has been a pioneer in this field and has demonstrated the usefulness of the antisense tehcnology for medicinal science. However, after three years of use, fomivirsen has been withdrawn from the market (in the US in 2001 and in the EU in 2002), and nowadays, gene silencing drugs with a more advanced chemical structure and more complex mechanism of action are used in medicine. On the occasion of the 20th anniversary of its European withdrawal, we briefly overview the history of fomivirsen. Kulcsszavak: fomivirsen, antisense, oligonucleotide, phosphorothioate, Vitravene