Middle East Respiratory Syndrome (MERS), Severe Acute Respiratory Syndrome (SARS) and Coronavirus Disease 2019 (COVID-19) are caused by three distinct coronaviruses belonging to the same genus. COVID-19 and its two predecessors share many important features in their clinical presentations, and in their propensity for progression to severe disease which is marked by high rates of morbidity and mortality. However, comparison of the three viral illnesses also reveals a number of specific differences in clinical manifestations and complications, which suggest variability in the disease process. This narrative review delineates the pulmonary, cardiac, renal, gastrointestinal, hepatic, neurological and hematologic complications associated with these three respiratory coronaviruses. It further describes the mechanisms of immune hyperactivation-particularly cytokine release syndrome-implicated in the multi-organ system injury seen in severe cases of MERS, SARS and COVID-19.