BACKGROUND AND OBJECTIVES: The second derivative of a photoplethysmogram (SDPTG) is a simple, convenient and non-invasive technique for pulse wave analysis. The SDPTG index correlates with age and other risk factors of atherosclerosis in the Japanese population, but has not yet been described in the Korean population. The purposes of this study were to analyze the age-related changes in the SDPTG of healthy subjects (study 1), and investigate the differences in the SDPTG of patients with hypertension, compared with those of normotensive subjects (study 2). We also compared the differences in the SDPTG between coronary artery disease (CAD) patients and normal subjects (study 3), to test the clinical usefulness of SDPTG in the evaluation of atherosclerosis. SUBJECTS AND METHODS: We consecutively studied 235 healthy adults, 40 with essential hypertension and 42 with CAD. Their SDPTG were recorded in the sitting position using a Fukuda FCP-3166. RESULTS: In study 1, the b/a ratio increased with age, whereas the c/a, d/a and e/a ratios decreased. The SDPTG aging index (AGI)(y) increased with age (x)(r=0.71, p=0.000;y=22.731x+54.571). In study 2, the patients with hypertension showed a lower average d/a ratio (-0.47+/-0.15 vs. -0.38+/-0.15, p=0.02) and higher average SDPTG AGI (-0.09+/-0.34 vs. -0.26+/-0.37, p=0.011) than the normotensive subjects. In study 3, the patients with CAD had higher average b/a ratio (-0.47+/-0.19 vs. -0.59+/-0.17, p=0.001) and SDPTG AGI (-0.01+/-0.41 vs. -0.23+/-0.40, p=0.004) than the normal subjects. In a logistic regression analysis, the SDPTG AGI was a significant determinant of CAD (p=0.046). CONCLUSION: The SDPTG aging index may be useful in the evaluation of vascular aging and damage due to hypertension and atherosclerosis.