Our objective was to evaluate the associations of the systolic and diastolic blood pressure night-to-day ratios (SBP-NDR and DBP-NDR) with composite atherosclerotic cardiovascular diseases (ASCVDs) comprising coronary heart disease (CHD) and ischemic stroke (IS) cases, respectively. The clinical conditions associated with SBP-NDR and DBP-NDR were also evaluated. A total of 401 patients who underwent 24-h ambulatory BP monitoring were enrolled. In general, the mean age was 59.7±14.7 years and male subjects accounted for 59.1% of the study subjects. Regarding the ASCVD risk factors, 17.0% of the study subjects smoked, 5.2% abused alcohol, 2.0% had a family history of ASCVD, 23.3% had diabetes and 96.0% had dyslipidemia. Fifty (12.5%) and 128 (31.9%) study subjects had a previous diagnosis of CHD and IS, respectively. Dipper and non-dipper pattern-specific differences in clinical characteristics between the SBP-NDR and DBP-NDR categories were observed. The multiple linear regression analysis showed that advanced age, smoking, CHD and IS were positively associated with SBP-NDR and statins were inversely associated with SBP-NDR; only IS was positively associated with DBP-NDR. The logistic regression analysis showed that after adjusting for the covariates of age, smoking, alcohol abuse, diabetes, hypertension, dyslipidemia, and SBP and DBP at admission, only DBP-NDR remained significantly associated with composite ASCVD, with an odds ratio of 1.029 (95% confidence interval 1.002-1.056, P=0.038). There were significant differences in the associations of SBP-NDR and DBP-NDR with composite ASCVD. Clinical conditions independently associated with SBP-NDR and DBP-NDR were also somewhat different. In a specific population group, DBP-NDR may be superior to SBP-NDR with respect to screening for ASCVD.