Obesity is a risk factor for disease severity in individuals with coronavirus disease (COVID-19). However, the increased susceptibility of this population to COVID-19 is unclear. We outline several underlying mechanisms that may explain the relationship between obesity and COVID-19 severity. Obesity has an adverse effect on respiratory physiology because increased intra-abdominal adipose tissue can interfere with lung expansion, resulting in a reduced lung compliance. Further, fat accumulation in the soft tissue of the pharynx can increase inspiratory resistance. Also, obesity may be associated with sleep apnea. Obesity is associated with several defects in cell-mediated immunity including increased levels of pro-inflammatory cytokines. Impaired adipocyte-mediated immune function results in chronically high leptin levels and low adiponectin levels and anti-inflammatory adipokines. Reduced physical activity can impair several steps of the immune response to viruses. Obesity also promotes a hypercoagulable state, leading to serious consequences. These factors may synergistically play a role in promoting the severity of the disease in obese individuals. A better understanding of the mechanisms by which obesity contributes to the severity of COVID-19 is important for developing more effective treatments.