Aspirin (ASA) has been shown to provide marked benefits in primary and secondary prevention of cardiovascular events. Substantial evidence suggests that low-dose ASA therapy should also be used as a primary prevention strategy in men and women with diabetes who are at high cardiovascular risk. On the other hand, there is current evidence on the potential benefits of low-dose ASA therapy in subjects with impaired fasting glucose, including those with metabolic syndrome. Most important, previous laboratory animal and clinical trial research convincingly demonstrates administration time-dependent (with reference to circadian rhythms) effects of ASA. Thus, the effects of ASA upon lipoperoxides, b-adrenergic receptors, and blood pressure (BP) in clinically healthy subjects depend on the circadian timing of ASA administration. The administration-time-dependent influence of ASA on BP was previously demonstrated in a randomized trial on healthy women and other independent double-blind, randomized, placebo-controlled clinical trials conducted, first, on clinically healthy subjects, a second one on normotensive and hypertensive subjects, a third one on pregnant women at high risk for preeclampsia and a fourth one in previously untreated patients with mild hypertension. The findings of these BP studies are consistent; BP-lowering effect of low-dose ASA is achieved when administered at bedtime but not upon awakening.