A total of 181 faecal samples were collected from wild cervids in two regions of Poland. Giardia cysts were detected in one faecal specimen from red deer and in two samples from roe deer. Fragments of the beta-giardin (bg) triose phosphate isomerase (tpi) and glutamate dehydrogenase (gdh) genes were successfully amplified from the Giardia isolate obtained from red deer, whereas only amplicons of bg and gdh were obtained from Giardia isolates derived from two roe deer. The result of genotyping and phylogenetic analysis showed that the G. duodenalis isolate from red deer belonged to sub-assemblage AIII, which has never been identified in humans, whereas isolates from roe deer clustered within zoonotic sub-assemblage AI. Further studies are necessary to explain which Giardia assemblages and/or sub-assemblages occur in wild cervids in various regions of the world. Moreover, the impact of Giardia infection on the health of wild cervids should also be elucidated.