Associations of Parkinson's disease (PD) with diabetes mellitus (DM) and other medical conditions were investigated in a case-control study of 352 newly diagnosed PD case and 484 control subjects. Men with DM had a significantly lower risk of PD, than men without DM (odds ratio (OR) = 0.52, 95% confidence interval (CI) = 0.28, 0.97), whereas the association in women was weaker (OR = 0.80, 95% CI = 0.35, 1.83). PD risk was reduced among male and female smokers, with and without diabetes. However, among diabetics, the PD risk was especially reduced in non-smoking men (OR = 0.09, 95% CI = 0.02, 0.44). Other medical conditions showed no strong relations with PD.