Background: Anxiety is an un-pleasurable emotional state associated with psychophysiological changes in response to an intrapsychic conflict. The perioperative period is one of the worrying events for most surgical patients. Despite preoperative anxiety having many negative consequences on post-operative physical and mental health, no adequate information on the degree to which the preoperative period exposed clients to preoperative anxiety and its associated factors. Objective: To assess the prevalence of preoperative anxiety and associated factors among adult surgical patients in Debre Berhan Comprehensive Specialized Hospital, Ethiopia. Methods: Institution-based cross-sectional study was conducted from June 1, 2020, to August 30, 2020. State-Trait Anxiety Inventory Scale (S-STAI) was used to measure the level of pre-operative anxiety. A systematic random sampling technique was employed to collect the data. The data were entered to Epi-Data version 4.6 and exported to SPSS version 25 for data analysis. A statistically significant association was declared at a p-value less than 0.05. Results: A total of 330 patients were enrolled in the study with a response rate of 93.2%. The prevalence of a high level of preoperative anxiety was 53.6% (95% CI (49.6-58.7)). Being female 3.2 (2.19, 3.71) illiterate 4.1 (2.01, 15.39), fear of death 2.12 (1.30, 3.44), results of operation 2.60 (1.75, 4.18), postoperative pain 2.35 (1.37, 4.02), and surgical complication 1.9 (1.03, 12.13) were statistically significant factors. Conclusion:Preoperative anxiety affects more than half of surgical patients which is a high and serious health burden. Additionally, this study revealed that being female, illiterate, fear of death, having a history of surgical complications and fear of complications, and fear of postoperative pain were significantly associated with preoperative anxiety. Assessing during the preoperative period helps to detect and ameliorate the problem. Preoperative counseling and informed consent taken as a prerequisite for surgery will help in reducing preoperative anxiety.