In December 2019, a new coronavirus identified, named SARS-CoV-2, as a factor in the investigations conducted on the reporting of viral pneumonia cases in the Wuhan city of China, and the disease called "Coronavirus Disease 2019 (COVID-19)". Chronic diseases take the first line among the risk factors that increase the case fatality rates in COVID-19 outbreak worldwide. Chronic diseases that progress slowly, last for three months or more, caused by over one risk factor, usually show a complicated course and affect the quality of life of the person. In fact, chronic diseases caused a silent global epidemic, and together with the COVID-19 pandemic, they prepared a ground that increased the effects of the pandemic. The first data of COVID-19 increased our knowledge about the clinical characteristics of the disease and pointed out that the disease is more frequent and more severe in individuals with chronic disease. In this article, the literature information on the most common chronic diseases, with important role in COVID-19 course and mortality, is given.