A new species of Mycetophilidae (Diptera), Acomopterella martinovskyi sp. n., is described from the Czech Republic and Austria. This is the first record of the genus from the Palaearctic region. Its relationships with other genera and variation in wing characters are briefly discussed. A new combination and synonymy is proposed: Acomopterella fallax (Sherman, 1921) comb.n. = Acomopterella arnaudi Zaitzev, 1989 syn.n.