In the past few decades, a number of epidemiologic studies have identified risk factors for the development of allergic disease. Although both maternal and paternal history of allergy are associated with an increased risk of atopy, maternal history of asthma confers the greater risk for childhood asthma, which suggests that environmental factors such as the in utero immunologic environment may confer additional susceptibility. Cytokine profiles at birth may also indicate a predisposition to allergic disease in later childhood. Specifically, low interferon-γ appears to be associated with an increased risk for later development of allergic symptoms and atopic disease. Allergen exposure may also increase the risk of atopic consequences, but the outcome is highly dependent on dose of the allergen, timing of exposure, and, most interestingly, the nature of the allergen in question. Endotoxin exposure during infancy has been associated with increased wheezing during the first years of life, but several studies indicate that early exposure may confer some protection against allergy later in life. Clearly, all these factors should be evaluated in identifying the appropriate prevention measures and treatment for the child who is at risk for allergic disease.