Objectives: The primary aim of this study was to assess the prevalence of sinus tracts in endodontically treated teeth in an Iranian population. The second aim was to seek and analyze the relationship between the clinically detected sinus tracts and factors such as sex, age, tooth type and location. Study design: A total of 728 patients` records and radiographs were reviewed of 427 females and 301 males for demographic data, preoperative pulpoperiapical status of treated teeth and the presence of sinus tract. Data were analyzed using chi-square test. Results: No significant differences were found for the prevalence of sinus tracts between two genders. Data showed that the highest prevalence of sinus tracts was in 10-19 year age group. Of 725 treated teeth, 107 teeth had sinus tracts (14.7%). Most odontogenic sinus tracts were associated with mandibular anterior teeth. Of 348 teeth with preoperative status of periapical inflammation and radiolucency, 107 teeth (30.75%) had an odontogenic sinus tract. Conclusion: Data showed that almost one in seven teeth referred for root canal treatment had a sinus tract.