Introduction: Endoscopy is an invasive diagnosis and treatment method which is stressful for patients. Previous studies have exhibited different results about the factors associated with anxiety of patients undergoing endoscopy. The aim of this study was to assess the predicting factors of patients' anxiety undergoing endoscopy.

Methods: This descriptive analytical study was conducted on 400 patients. The method was continuous sampling. The data-gathering instrument was researcher made and consisted of three parts; demographic information, questions relating to awareness about endoscopic method, and Spielberg’s questionnaires for assessing patients' state anxiety. Data were analyzed with t-tests, ANOVA and Pearson’s correlation and regression logistic.

Results: From these number of patients, 82.7% had moderate to severe anxiety. There was a significant relationship between marital status and level of anxiety in patients (P = 0.02). Also, there was a significant relationship between patients’ anxiety scores and their knowledge scores. Regression results showed that marital status, type of admission and endoscopic history were predictive factors for patients' anxiety.

Conclusions: Most patients have moderate to severe anxiety before endoscopy. Lack of knowledge of patients about endoscopy methods is a major cause of anxiety. Since severe anxiety can have an impact on correct performance of endoscopy as well as on patients' outcome, proper measures need to be taken to raise patients' awareness.