A novel coronavirus was identified in Wuhan in December 2019 and it rapidly spread throughout China, followed by in other countries. The aim of this study is to investigate the effects of comorbidities on patients with COVID-19 and to give information about their management. The electronic databases PubMed and Google Scholar have been used to assess comorbidities and clinical characteristics of COVID-19. Severe disease predominantly occurs in adults with underlying medical comorbidities or advanced age. Comorbidities and other conditions that associated with morbidity and mortality include hypertension, diabetes mellitus, cardiovascular disease, chronic lung disease, cancer (particularly metastatic disease, lung cancer, and hematologic malignancies) and chronic kidney disease. As the number of comorbidity increases, patients' clinic progresses more severely. A comprehensive assessment and good management of comorbidities can help patients with COVID-19 achieve a better outcome.