This study was performed to investigate the relationship between reversed circadian blood pressure and risk factors of peripheral vascular disease in non-insulin-dependent diabetes mellitus (NIDDM) subjects. The subjects in this study were 18 NIDDM patients who were hospitalized in a medical unit of an university medical center located in Incheon, Korea, between November, 1998 and March, 1999. Blood pressure was measured with a mercury sphygmomanometer by 2 trained examiners every 2 hours during 24 hours. NIDDM subjects were divided into a dipper group and non-dipper group. Dippers are defined as those who show a mean nighttime blood pressure(BP) drop of more than 10% compared with daytime BP. Non-dippers are defined as those who show a mean nighttime BP drop of less than 10%, or an elevation in BP compared with daytime BP. Daytime BP included values obtained between 6 a.m. and 10 p.m. Night time BP included values obtained between 10 p.m. and 6 a.m. Data was analyzed by SPSS/PC package. Chi-square( 2) test was used for the comparison of sex between The dipper group and non-dipper group. Mann-Whitney test was used for comparisons of values of the risk factors of peripheral vascular disease and the frequency of complications of diabetes between the dipper group and non-dipper group. The results are as follows. There were no significant differences in daytime systolic, diastolic, and mean blood pressures between the dipper group and non-dipper group. However, night time systolic, diastolic, and mean blood pressures in the non-dipper group were significantly nigher than those in the dipper group (p=.021). There were no differences in sex, age, body, weight, duration of diabetes, serum lipid levels, BUN and HbA1c between the two groups. On the contrary, 87.5% of non-dipper group subjects showed having hypertension, 30% of dipper group subjects showed having hypertension and this difference was statistically significant (p=.018). All of the non-dipper group subjects (N=8) showed having at least one diabetic complication. However, 40% of the dipper group subjects (N=10) showed having no diabetic complication at all and this difference was also statistically significant (p=.049). There were no significant differences in frequency of nephropathy, neuropathy and retinopathy between the dipper group and non-dipper group.