The castor bean tick, Ixodes ricinus, is common in woodlands in most of Denmark. Besides Borrelia burgdorferi, it can harbour a number of pathogenic microorganisms such as tick-borne encephalitis virus, Anaplasma phagocytophilum, Rickettsia helvetica, Francisella tularensis, Candidatus Neoehrlichia mikurensis, Bartonella spp., Borrelia miyamotoi and Babesia spp. These tick-borne infections should be a differential diagnostic consideration during the tick season in Denmark. We review the distribution, clinical manifestations, diagnosis and treatment of these microorganisms.