Background: Chronic pesticide exposure is a recognized risk for human health. The frequency of congenital malformations in exposed people, can be used for epidemiological studies assessing reproductive risk secondary to toxic exposure. Aim: To study the association between the incidence of congenital malformations and parent s exposure to pesticides. Material and methods: A prospective study of cases and controls. The exposure could be caused by occupational activities or residence around fumigated crops. The records of cases and controls from the surveillance carried out in the Hospital Regional de Rancagua were analyzed. This hospital is active member of a collaborative study of congenital malformations in Latin America. Results: In two years there was a total of 453 newborns (18 stillborn) with congenital malformations, with an incidence of 41.24 . Considering only children born alive, the paired analysis of cases and controls showed an association of congenital malformations with a history of maternal exposure, with an attributable fraction of 54.4%. Conclusions: These results, showing an association between pesticide exposure and congenital malformations, should be analyzed in the future by a logistic regression test. (Rev Méd Chile 2000; 128: 399-404)