The importance of early life environmental influences on the etiology of asthma is implied by the observed geographic and temporal variation in the prevalence of the disease among children. There is evidence pointing to the role of exposure to allergen, various aspects of diet and hygiene-related factors in the etiology of asthma. There is also evidence that heritable factors influence the impact of hygiene-related exposures on the risk of having asthma. A number of important gene-environment interactions have been identified. These interactions point to the biology of environmental exposures as the involved genetic variation is suggestive of certain underlying mechanisms. Polymorphisms within genes coding for the toll-like receptor-lipopolysaccharide (TLR-LPS) signalling pathway may underlie variations in effects of hygiene-related exposures, including specifically endotoxin, on the risk of developing allergic sensitization and allergic disease. This review presents recent findings illustrating the role of gene-environment interactions in childhood asthma susceptibility.