The first disputes that the nascent League of Nations had to deal with came from the Baltic sea region. While the successful settlement of the Aland Islands dispute is well known and quoted in international legal textbooks, League's mediation in the Vilnius dispute between Lithuania and Poland received much less scholarly attention. This paper will try to assess the League's involvement in the Vilnius conflict beyond the traditional success-failure dichotomy, emphasizing the extent of international cooperation achieved in organizing the plebiscite, as well as looking at how this case shaped the League itself.