In music, Op. 90 stands for Opus number 90. Compositions that are assigned this number include:
Beethoven – Piano Sonata No. 27 Brahms – Symphony No. 3 Dvořák – Piano Trio No. 4 Klebe – Die Fastnachtsbeichte Mendelssohn – Symphony No. 4 Schubert – Impromptus Schumann – 6 Gedichte und Requiem Sibelius – Six Runeberg Songs, collection of art songs (1917)