This paper describes morphological characteristics and the occurrence of Demodex corniculatus n. sp., which was found on Apodemus flavicollis in Poland. The yellow-necked murid mouse is a common European rodent; until now, it was parasitized by a single demodectic mite species, Demodex rosus, which occurs in the oral cavity and esophagus. The new species was found in hair follicles, particularly within hairy regions of the head and genital–anal area. Demodex corniculatus occurred in 33% of the yellow-necked mice examined. The new species is small (adult stages 140 μm in length); characteristic features of these mites are massive supracoxal spines (ca. 5–6 μm long) on the dorsal side of the gnathosoma and palps with thick-set, bifurcated terminal spines. This paper also contains a checklist of demodecids in European and cosmopolitan murids.