Background. A strong link between morbidity andmortality from COVID-19 and diabetes mellitus is reported by many studies. The present study estimated the pooled prevalence of diabetes in patients with COVID-19. Methods. International scientific databases were searched until 15 April 2020. There was no limitation in time and language of the published papers. Quality assessment of studies was performed using the Newcastle-Ottawa Scale (NOS) checklist. The random effects model was used to report the pooled prevalence with 95% confidence interval (CI). Results. The pooled prevalence of diabetes in patients with COVID-19 was 14% (95% CI: 11.17). Due to high heterogeneity (I2 of 93.4%, P < 0.001), three subgroups were analyzed based on study location, age and sex. The prevalence of diabetes (P) was higher among male patients (P = 16%, 95% CI: 0.12, 0.20), patients aged ≥ 65 years (P = 19%, 95% CI: 0.08, 0.31). The prevalence of diabetes was 15% (95% CI: 0.10, 0.20) among patients in Wuhan, China and 10% in patients in other cities in China (95% CI: 0.06, 0.15), and 39% in patients from other countries (95% CI: 0.04, 0.74). Conclusion. According to the results of this systematic review, the prevalence of diabetes in patients with COVID-19 is higher in other countries compared to China. The prevalence of diabetes among COVID-19 patients was also significantly higher in men and elderlies. This evidence may be useful for health policymakers to design suitable preventive and therapeutic interventions in patients with diabetes and COVID-19.