Parkinson's disease, the primary cause of parkinsonian syndrome, is, after Alzheimer's disease, the most frequent neurodegenerative disorder. Parkinson's disease is currently considered as a multifactorial disease resulting from the effect of genetic and environmental susceptibility. Several epidemiological studies have shown a moderate association between Parkinson's disease and farmer occupation or exposure to pesticides. Nevertheless, no product has been incriminated in a repeatable manner in these studies. The main methodological difficulty of these studies is associated with the complexity in assessing the occupational exposure to pesticides. The results of the toxicological studies point equally in this direction and provide arguments in favor of this relationship. However, some questions remain to be answered, particularly the role of low-dose exposure, the gene-environment interactions and the implied biological mechanisms.