In this study, we report a large family cluster consisting of 29 genetically related patients hospitalized with coronavirus disease-2019 (COVID-19). We sought to determine the clinical characteristics relevant to the clinical course of COVID-19 by comparing the family cluster to unrelated patients with SARS-CoV-2 infection so that the presence of potential determinants of disease severity, other than traditional risk factors previously reported, could be investigated. Twenty-nine patient files were investigated in group 1 and group 2 was created with 52 consecutive patients with COVID-19 having age and gender compatibility. The virus was detected for diagnosis. The clinical, laboratory and imaging features of all patients were retrospectively screened. Disease course was assessed using records regarding outcome from patient files retrospectively. Groups were compared with respect to baseline characteristics, disease severity on presentation, and disease course. There was no difference between the two groups in terms of comorbidity and smoking history. In terms of inhospital treatment, use differed not significantly between two groups. We found that all 29 patients in the group 1 had severe pneumonia, 18 patients had severe pneumonia. Hospitalization rates, length of hospital stay, and transferred to intensive care unit were found to be statistically significantly higher in the group 1. In the present study, COVID-19 cases in the large family cluster were shown to have more severe disease and worse clinical course compared with consecutive patients with COVID-19 presenting to the same time. We believe further studies into potential genetic mechanisms of host susceptibility to COVID-19 should include such family clusters.