AIMS: Diabetes mellitus (DM) is associated with significant morbidity and mortality. The disease severity in 2019 novel coronavirus (Covid 19) infection has varied from mild self-limiting flu-like illness to fulminant pneumonia, respiratory failure and death. Since DM and Covid 19 infection are closely associated with inflammatory status, mean platelet volume (MPV) was suggested to be useful in predicting Covid infection onset. This study aimed to evaluate the diagnostic role of MPV in Covid patients with diabetes. METHODS: A total of 640 subjects (160 Covid patients with type 2 diabetes, 160 healthy controls, 160 patients with non-spesific infections and 160 Covid patients without type 2 diabetes) enrolled in the study. RESULTS: MPV was significantly higher (11.21 +/- 0.61 fL) as compared to the results from the last routine visits of the the same individuals with diabetes (10.59 +/- 0.96 fL) (p = 0.000). CONCLUSIONS: MPV could be used as a simple and cost-effective tool to predict the Covid infection in subjects with diabetes in primary care.