Pesticides are chemicals that are widely used all over the world. Human beings can be exposed through environmental contamination and/or occupational use of pesticides. Although there is substantial information on the acute toxicity of many of these chemicals, available knowledge on delayed effects is much more limited. This paper reviews epidemiological studies on occupational exposure to pesticides, mainly in agricultural workers, and risk of congenital malformations. The discussion includes postulated mechanisms for birth defects from paternal or maternal exposure, a detailed review of method of the studies carried out so far on the relationship between occupational exposure to pesticides and congenital malformations, and a summary of main results obtained. From available information, it seems reasonable to conclude that, to date, there is inadequate evidence for either establishing a relationship between pesticides exposure in human beings and birth defects or for rejecting it. Avoiding the main limitations of previous studies, some of the key elements for future research are presented.