Sirtuin 1 (SIRT1), a member of the silent information regulator 2 in mammals, has recently been found to be involved in age-related diseases, such as cancer, metabolic diseases, cardiovascular disease, neurodegenerative diseases, osteoporosis and chronic obstructive pulmonary disease (COPD), mainly through deacetylation of substrates such as p53, forkhead box class O, peroxisome proliferator activated receptor gamma co-activator 1alpha, and nuclear factor-kappaB. It is widely reported that SIRT1 can promote not only carcinogenesis but also metastasis and insulin resistance, andhave beneficial effects in metabolic diseases, mediate high-density lipoprotein synthesis and regulate endothelial nitric oxide to protect against cardiovascular disease, have a cardioprotective role in heart failure, protect against neurodegenerative pathological changes, promote osteoblast differentiation, and also play a pivotal role as an anti-inflammatory mediator in COPD. However, there are controversial results suggesting that SIRT1 has an effect in protecting against DNA damage and accumulation of mutations, and preventing tumorigenesis. In addition, a high level of SIRT1 can induce cardiomyopathy and even heart failure. This article reviews recent developments relating to these issues.