Recent evidence suggests that proximity to pets and farm animals early in life may decrease the risk of developing atopy. Studies investigating the etiology of atopy and asthma have been especially challenging due to difficulties in ascertaining and classifying incident cases. Nevertheless, cross-sectional and cohort studies described in this paper reported across various populations, among children and adults, tended to demonstrate inverse associations between the presence of indoor cats and dogs or frequent exposure to livestock during the first years of life and sensitization to pet and pollen allergens, hay fever, and to a lesser degree, asthma. The biological mechanisms of this protection is unknown, as are the factors associated with pet keeping and livestock farming that may play a role. In the meantime, it appears that counseling prospective parents that avoidance of exposure to animals in the first years of life will prevent atopy may not be sage advice.