Marasmius celtibericus G. Moreno & Raitviir, a new species from Spain, is described and illustrated. It is characterized by very small basidiocarps with a smooth hymenophore, somewhat resembling Marasmius cornelii Laessøe & Noordel. Microscopically, however, Marasmius celtibericus must be ranged in sect. Hygrometrici on account of the pileipellis.