Abstract The worldwide spread of coronavirus disease 2019 (COVID-19) has generated a global health crisis and more than a million deaths so far. Epidemiological and clinical characteristics of COVID-19 are increasingly reported, along with its potential relationship with overweight and/or obesity. Therefore, we aim here to review the current scientific literature on the impact of overweight and/or obesity among hospitalized patients who have developed severe or critical forms of COVID-19. Following PRISMA guidelines, our literature search identified over 300 scientific articles using the keywords “obesity” and “COVID-19”, 22 of which were finally selected for reporting useful information on the association between overweight/obesity and disease severity. In particular, in 11 out of the 14 studies (79%) which evaluated the association between obesity and disease severity providing also a risk estimate (i.e., the odd ratio; OR), the OR value was constantly >2. Although the studies were found to be heterogeneous in terms of design, population, sample size and endpoints, in most cases a significant association was found between obesity and the risk of progressing to severe COVID-19 illness, intensive care unit admission and/or death. We can hence conclude that an increased body mass index shall be considered a negative prognostic factor in patients with COVID-19, and more aggressive prevention or treatment shall hence be reserved to overweight and/or obese patients.