We report the discovery of the pyrophilous species, Asemum tenuicorne (Coleoptera: Cerambycidae) in the Białowieża Primeval Forest (NE Poland) in 2009 and 2016. This species was previously known only from Southern Europe and one locality detached from the main range on the island of Gotska Sandön in Southern Sweden. Information on its northern spread and current distribution is summarized and critically analyzed and new data on its biology are provided. The morphology of A. tenuicorne adults was studied using 46 specimens from different localities and compared with 63 specimens of the widely distributed Asemum striatum. Differences between the two species are presented and illustrated using external features, morphometric measurements, shape of the male copulatory organs and wing venation.