Although haemobartonellosis was previously reported in Hungary, until now the diagnosis (based on morphological identification in blood smears) has only been suggestive of the occurrence of the large species, recently reclassified as Mycoplasma haemofelis. However, in July 2007 a cat was presented at a small animal clinic with severe haemolytic anaemia, icterus and haemoglobinuria. While biochemical parameters were within the reference range, the cat had leukocytosis and rapidly decreasing haematocrit values, and eventually died 7 days after the sudden onset of aggravating clinical signs. From blood samples of the cat 'Candidatus Mycoplasma haemominutum' was identified by molecular methods, according to its 100% 16S rRNA gene sequence homology with two Swiss isolates and one isolate from the UK. The rapid termination of the disease and the high pathogenicity of the causative agent observed in this case are unusual, taking into account that PCR results were negative for immunosuppressive viruses. This is the first record of this feline haemoplasma species in Hungary.