The occupational history of the parents of 261 infants with congenital malformations and 261 matched controls was collected. During the relevant time period before the birth of their child, 183 parents were involved in agricultural activities, 49% of them having directly applied pesticides. Two experts assessed the probability and the level of exposure to each quoted pesticide (582 observations) by using 4-point scales. Interrater agreement was estimated. Kappa-weighted values for probability and level of exposure were, respectively, kappa = 0.36 and kappa = 0.39. In the analysis of some categories of exposure (non-applicators, herbicides) very low interrater agreement was observed. In epidemiological studies, detailed assessment of pesticide exposure (product-by-product) is needed to investigate the effects of pesticides on health. But the application of experts' judgment in this area needs more research in assessing the validity of this approach.