Background: Mucormycosis has abruptly increased in Egypt during the third wave of COVID-19 especially in patients with diabetes mellitus (DM). The aim of this study was to investigate the risk factors, clinical presentation and outcome of mucormycosis in COVID-19 patients with diabetes. Methods: Prospective cohort study was conducted on 72 COVID-19 patients with DM presented with mucormycosis at intensive care units and Ear, Nose, and Throat Department of Zagazig University Hospitals over a period of three months from May 2021 to August 2021. All participants were submitted to history taking, examination, laboratory investigation, radiological and histopathology and culture testing. Results: Post COVID-19 new-onset diabetes mellitus (NOD) was detected in 40% of studied patients. 72.2% of patients had poorly controlled diabetes. Majority of studied patients presented by rhino-orbital mucormycosis (90.3%) and about 86% of them were operated. Hundred percent of patients gave history of antibiotic use and also nearly 99.0% of them received corticosteroids, while only 1.4% of them received tocilizumab. There was statistically significant association between operated patients, hemoglobin (HB) level, lymphocyte count, neutrophil-lymphocyte ratio (NLR), and CRP level with disease prognosis. Conclusions: Poorly controlled DM and steroid use are the most important risk for post COVID-19 mucormycosis. Early surgical intervention carried better disease outcome.