This is the first investigation of Giardia prevalence in farm animals and in farmers or their family members in Poland. The prevalence of infection was 1.3% in sheep and 2.2% in cattle. Thus, infection rates of livestock in Poland are much lower than those recorded by investigators in other countries. Moreover, we recognized Giardia infection both in human and calf in the same time and place. This strong evidence of zoonotic transmission is discussed in the present paper.