Approximately 400,000 workers in the United States are employed as welders, cutters, solderers, and brazers, and about 5 million workers worldwide are exposed to welding aerosols daily; though considered controversial, welding and occupational exposure to manganese fumes have been associated with Parkinson’s disease and/or Parkinsonism, and concern for these exposures as possible risk factors for these diseases continues in spite of recent negative findings. [Note: Parkinson’s disease is a separate condition from manganism, a disease caused by high-dose manganese exposures.] The purpose of this assessment was to conduct a causation analysis using the principles of Evidence-based Toxicology (EBT) and Evidence-based Medicine (EBM), a process that provides a systematic, transparent, and objective procedure for evaluating whether occupational exposure manganese fumes or welding should be considered a known cause of Parkinson’s disease. As part of our analysis, we conducted a comprehensive literature search from which we identified 4 cohort, 10 case-control, and 3 registry-based studies that met the inclusion criteria. Case reports, case series, cross-sectional and ecological studies were excluded because they are hypothesis-generating and do not provide evidence for causation. The studies were ranked according to their basic epidemiological design, and then each was scored according to a set of a priori criteria.  The overall analyses showed study findings were largely negative and that the negative studies had higher rating scores than did the few studies reporting positive findings. The outcome of this EBT analysis demonstrates the currently available epidemiological data do not support that either welding or occupational exposure to manganese fumes is a cause of Parkinson’s disease in humans.