•Severe COVID-19 patients present overwhelming inflammatory reactions leading to lung injury.•Corticosteroids may beneficially modulate the host immune response to COVID-19 pneumonia.•Before–after study evaluating the effect of corticosteroid addition to COVID-19 pneumonia treatment on hospital mortality.•In multivariate analysis, the ‘after’ period was associated with an adjusted lower risk of death (aHR = 0.47; P = 0.04).•‘After’ period was also associated with lower risk of ICU admission or death before ICU admission (aHR = 0.37; P < 0.001). Anti-inflammatory drugs such as corticosteroids may beneficially modulate the host inflammatory response to coronavirus disease 2019 (COVID-19) pneumonia. The aim of this study was to evaluate the impact of addition of corticosteroids to the hospital protocol for treatment of suspected or confirmed COVID-19 pneumonia on rates of death or intensive care unit (ICU) admission. A before–after study was performed to evaluate the effect of addition of corticosteroids to our institution's COVID-19 treatment protocol on hospital mortality. A total of 257 patients with a COVID-19 diagnosis were included in this study between 3 March 2020 and 14 April 2020. As corticosteroids were widely used after 27 March 2020, two periods were considered for the purposes of this study: the ‘before’ period from 3–20 March 2020 (n = 85); and the ‘after’ period from 26 March–14 April 2020 (n = 172). The ‘after’ period was associated with a lower risk of death adjusted hazard ratio (aHR) = 0.47, 95% confidence interval (CI) 0.23–0.97; P = 0.04 and a lower risk of ICU admission or of death before ICU admission (aHR = 0.37, 95% CI 0.21–0.64; P = 0.0005) by multivariate analysis adjusted for age, National Early Warning score and institutionalisation status. In conclusion, addition of corticosteroids to our institution's COVID-19 treatment protocol was associated with a significant reduction in hospital mortality in the ‘after’ period.