ABSTRACT:Background:The age-at-onset (AAO) of Parkinson’s disease (PD) is thought to be influenced by environmental factors and polygenic predispositions. Professional exposures to pesticides and toxic metals were shown to be associated with an earlier onset in small sample studies.Aim of Study:The aim of this study was to confirm the association between professional exposures to pesticides and toxic metals and the AAO of PD, on a larger cohort of patients, defined with a clinic-based ascertainment scheme.Methods:We used an incident cohort of 290 patients recruited through three designated movement disorder clinics in the province of Quebec, Canada. Patients completed a detailed questionnaire regarding professional exposures to pesticides and toxic metals. We compared the AAO in patients without prior professional exposure (N = 170) and those with exposure to pesticides (N = 53) or toxic metals through welding (N = 30). We further subdivided patients exposed to pesticides according to the frequency and proximity of their contacts.Results:Patients with prior exposure to pesticides (AAO = 54.74 years) or toxic metals (54.27 years) had a significantly earlier AAO compared to the control group (59.26 years) (p = 0.003). In those exposed to pesticides, closer (p = 0.03) and more frequent (p = 0.02) contacts were negatively correlated with AAO.Conclusion:Exposure to pesticides and toxic metals were both associated with an earlier onset of PD, an effect that was greater with higher levels of exposure, both in terms of frequency and proximity.