Job title or employment sector may be associated with Parkinson's disease (PD). Methods In a case-control study, in four European centres, lifetime occupational histories were coded using modified International Standard Industrial Classification (ISIC) and Dictionary of Occupational Titles (DOT). We employed multiple logistic regression analyses adjusting for age, gender, smoking and family history of PD. Results A total of 649 cases and 1587 controls were recruited. Scottish data showed a

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... ignificant increased risk for agriculture (DOT: OR 1.32, 95% CI 0.81-2.16; ISIC: OR 1.30, 95% CI 0.84-2.02) and reduced risk for 'transport and communication' (ISIC: OR 0.60, 95% CI 0.37-0.97). Subsequent four-centre analyses showed reduced risk for processing occupations (DOT: OR 0.69, 95% CI 0.5-0.95). An association with pesticide exposure, found using detailed exposure assessment, was not apparent using job classification. Conclusions In contrast to retrospective exposure assessment, job or industrial sector is a weak indicator of toxic exposures such that true associations may be missed.