Objective: An outbreak of coronavirus disease 2019 (COVID-19) occurred in late 2019. A better understanding of this disease will help us in preventing and managing it. This study evaluated the risk factors and clinical and laboratory characteristics of patients admitted to Shahid Sadoughi hospital in Yazd with a diagnosis of COVID-19. Methods: This cross-sectional study was conducted on patients with the diagnosis of COVID-19 admitted to Shahid Sadoughi hospital in Yazd in May 2020, Iran. Patients’ clinical information, including their symptoms at admission, history of smoking or drug/ alcohol abuse, history of Td (tetanus, diphtheria) vaccine, radiographic/computed tomography (CT) scan findings, and blood oxygen saturation, was recorded. The patients were also asked about their previous history of diabetes, hypertension, autoimmune disorder, and cancer or history of diseases in heart, lung, liver, and thyroid. Laboratory findings, height, weight and body mass index of the patients were also recorded. Statistical analyses were performed using SPSS 21. Results: The mean age of 86 patients enrolled in the study was 61.40±17.37 years, of which 56 (65.11%) had mild pulmonary involvement and 30 (34.89%) had severe pulmonary involvement, according to CT scan results. Also, 26 (30.2%) of all patients had diabetes and about 30 (36%) had high blood pressure, but current smokers (6%) were rare. In patients with severe pulmonary involvement, the level of neutrophil, creatinine, and lactate dehydrogenase (LDH) was higher than patients with mild pulmonary involvement. Out of 56 patients with mild pulmonary involvement, 47 patients had a history of Td vaccination in the last 5 years. Only one patient in the severe group had a history of Td vaccination. Conclusion: A lower percentage of blood lymphocytes as well as higher levels of neutrophils, creatinine, and LDH were observed in patients with severe pulmonary involvement. Numerous factors, especially more prominent laboratory abnormalities, determine the severity of the disease, and a better understanding of these factors can help physicians know the severity of the disease and its prognosis. These findings help us to further clarify the characteristics of COVID-19. Also, the effect of Td vaccine should be investigated in future studies.