ABSTRACT: Aims:We assessed the association between smoking status and mild cognitive impairment (MCI) in Japanese diabetic patients. Methods:This cross-sectional study included 323 diabetic patients, aged 40-79 years, who were referred to an outpatient diabetic clinic between January and July 2013 at Shiga University of Medical Science Hospital (Otsu, Japan). Cognitive function was assessed using the mini-mental state examination (MMSE), and patients were classified into two categories: normal cognitive function (MMSE score ?27) and MCI (MMSE score 22-26). Logistic regression analysis was used to estimate the multivariable-adjusted odds ratios (ORs) and 95 % confidence intervals (CIs) for MCI in current smokers and ex-smokers compared with never-smokers. Results:Of the 323 patients, 55 (17.0 %), 134 (41.5 %), and 134 (41.5 %) were current smokers, ex-smokers, and never-smokers, respectively. Of these, 68 (21.0 %) patients had MCI. After adjusting for age, sex, systolic blood pressure, body mass index, high-density lipoprotein cholesterol, estimated glomerular filtration rate, hemoglobin A1c, insulin therapy, sulfonylurea, history of coronary heart disease, exercise habit, drinking status, and education, the OR for MCI was 3.62 (95 % CI 1.26-10.40) in current smokers compared with never-smokers. In addition, the multivariable-adjusted ORs for MCI were 3.02 (95 % CI 0.64-14.32) in current smokers <30.0 pack-years and 4.90 (95 % CI 1.32-18.16) in current smokers ?30.0 pack-years, compared with never-smokers (p for trend = 0.017). Conclusions:Current smoking, especially current smoking for which cumulative lifetime exposure was high, was associated with MCI, as assessed using the MMSE in Japanese diabetic patients.