Abstract: This the first report on the presence of Ehrlichia cf. ewingii in a reindeer (Rangifer tarandus) in Hungary. The animal started to show apathy and loss of appetite and subsequently died shortly after being placed in an enclosure with dense vegetation, following a quarantine period. During the diagnostic necropsy, a large volume of reddish pericardial and thoracic effusion was observed resembling heartwater disease. Ehrlichia cf. ewingii was detected from the thoracic effusion by PCR and sequencing. The selenium content of multiple organs (liver, kidney, heart and skeletal muscles) were measured, but no increase was found. PCR tests for the detection of adenoviruses from the liver, lungs and spleen were negative. The routine bacteriological culture from the liver did not yield specific results either. To establish a causal relationship between the presence of E. cf. ewingii and the animal's death, further investigations are necessary.