Many studies have shown a protective effect of cigarette smoking on Parkinson  s disease. However, criticism has been raised concerning confounding by genet ic factors. We investigated the associations between Parkinson s disease and s moking, alcohol, coffee, area of living, and education in a co twin control st udy. Because twins are matched for genetic and familial environmental factors, t his design controls for confounding by these factors. We also examined control s ubjects unrelated to cases. Exposure information was taken from questionnaires a nswered in the 1960s and 1970s. Parkinson s disease cases were identified thro ugh the Swedish Inpatient Discharge Register (IDR) and the Cause of Death Regist er. In the unrelated control subject comparison, 476 Parkinson s disease cases and 2,380 control subjects were included. In the co twin control comparison, 415 same sex twin pairs were included. There was an inverse association betwee n smoking and Parkinson s disease using unrelated control subjects and co tw in control cases. There was no association between Parkinson s disease and alc ohol, coffee, or area of living. High educational level was associated with Park inson s disease in the unrelated control subject comparison but not in the co  twin control comparison. We confirm the protective effect of smoking on Parki nson s disease and establish that the association is only partially explained by genetic and familial environmental factors. Many studies have shown a protective effect of cigarette smoking on Parkinson’s disease. However, criticism has been raised concerning confounding by genet ic factors. We investigated the associations between Parkinson’s disease and s moking, alcohol, coffee, area of ​​living, and education in a co  twin control st udy. Because twins are matched for genetic and familial environmental factors, t his design controls for confounding by these factors. We also examined control s ubjects unrelated to cases. in the 1960s and 1970s. Parkinson’s disease cases were identified thro ugh the Swedish Inpatient Discharge Register (IDR) and the Cause of Death Regist er. In the unrelated control subject comparison, 476 Parkinson’s disease cases and 2,380 control subjects were included In the co-twin control comparison, 415 same-sex twin pairs were included. There was an inverse association betwee n smoking and Parkinson’ s disease using unrelated control subjects and co-tw in control cases. There was no association between Parkinson’s disease and alc ohol, coffee, or area of ​​living. High educational level was associated with Park inson’s disease in the unrelated control subjects we confirm the protective effect of smoking on Parki nson’s disease and establish that the association is only partially explained by genetic and familial environmental factors.