BACKGROUND: COVID-19 pneumonia is a newly recognized illness that is spreading rapidly around the world and causes many disability and deaths. Some diseases, for instance diabetes, is continuously suggested as a risk factor which contributes to the severity and mortality of COVID-19. However, to date, there are no comprehensive studies aiming to explain the exact relationship between diabetes and COVID-19. Thus, this study aims to summarize the evidence about diabetes and COVID-19 outbreak through a systematic review and meta-analysis approach. METHOD: A literature review was implemented within databases of Scopus, PubMed, Science direct, and Web of science. Observational reviews, case-report, and case-series studies that assessed the diabetes in COVID-19 patients, were included. Data extraction and assessment were guided by PRISMA checklist. FINDINGS: Some studies suggest that there were no significant differences in symptoms between patients who suffered from both diabetes and COVID-19 and those who only suffered COVID-19. In the subsequent meta-analysis 14.5% of the subjects were diabetic patient. These clients have poor ARDS prognosis, severe symptoms, and the death rate is higher among COVID-19 patients. In addition, it is suggested the diabetic patients will be treated with antibiotics, antivirals, and HCQ. CONCLUSION: The results of this study show that diabetes is a risk factor - and contributes to the severity and mortality of patients with COVID-19. This paper also provides recommendations and guidelines for which could be useful for prevention and treatment of diabetic patients affected by COVID-19.