In invasively ventilated COVID-19 patients, researchers investigated the prevalence of hypercapnia and its associations with outcome. A posthoc analysis of a national, multicenter observational study in 22 intensive care units. During the first 3 days of invasive ventilation, patients have been classified as ‘hypercapnic’ or ‘normocapnic.’ The primary endpoint was hypercapnia prevalence. Secondary endpoints included ventilator parameters, LOS in the ICU and hospital, and mortality in the ICU and hospital on days 28 and 90. About 485 (58.9%) of the 824 patients were hypercapnic. Hypercapnic patients had a higher BMI and were more likely to have COPD, severe ARDS, and venous thromboembolic events. Lower tidal volumes, higher respiratory rates, higher driving pressures, and more mechanical ventilation power were used to ventilate hypercapnic patients. Hypercapnic patients had comparable minute volumes but higher ventilatory ratios than normocapnic patients. Ventilation and LOS in ICU and hospital were longer in hypercapnic patients, but mortality was comparable to normocapnic patients. In invasively ventilated COVID-19 patients, hypercapnia was common. The main differences between hypercapnic and normocapnic patients were the severity of ARDS, the occurrence of venous thromboembolic events, and a higher ventilation ratio. Hypercapnia was associated with length of ventilation and length of stay in the ICU and hospital but not with mortality.