We conducted a systematic review of observational studies to examine the effects of body mass index (BMI) and obesity (BMI ≥ 30 kg/m) on coronavirus disease 2019 (COVID-19). Medline, Embase, and the Cochrane Library were searched . Sixteen articles were finally included in the meta-analysis, and a random effects model was used . BMI was found to be higher in patients with severe disease than in those with mild or moderate disease (MD 1.6 , 95% CI , 0.8-2.4; p = .0002) in China; however, the heterogeneity was high (I = 75 %). Elevated BMI was associated with invasive mechanical ventilation (IMV) use (MD 4.1 , 95% CI , 2.1-6.1; p <.0001) in Western countries, and this result was consistent across studies (I = 0 %). Additionally, there were increased odds ratios of IMV use (OR 2.0 , 95% CI , 1.4-2.9; p <.0001) and hospitalization (OR 1.4 , 95% CI , 1.3-1.60; p <.00001) in patients with obesity . There was no substantial heterogeneity (I = 0 %). In conclusion, obesity or high BMI increased the risk of hospitalization, severe disease and invasive mechanical ventilation in COVID-19 . Physicians must be alert to these early indicators to identify critical patients.