While a student, Olrik soon came under the influence of Svend Grundtvig, and until the latter's death in 1883, was treated almost like a son. His first major scholarly work was therefore a continuation of Grundtvig's work on the Danish ballads; with "Danske Ridderviser" (1898–1919) he continued the publication of "Danmarks gamle Folkeviser", which was in turn continued after his own death by his pupil Hakon Grüner-Nielsen. Olrik was able to draw more than Grundtvig on collected oral material; in 1888–89 he himself did some fieldwork collecting folksongs.