Background: Needle-Stick Injuries (NSIs) are among the hazards and problems that can expose health workers to infections. Objectives: This study aimed to determine the rate of NSIs in a teaching hospital in Tehran, Iran. Materials and Methods: This cross-sectional, analytical and descriptive study was conducted at one of the teaching hospitals in Tehran, Iran, in 2013. The study population was 344 employees in various occupational groups selected via census. Data were collected using a researcher-made questionnaire. The collected data were analyzed using some statistical tests, including independent-samples t-test with SPSS software version 21.0. Results: The results showed that only 50.2% of injuries had been reported; 67.8% of all participants (n = 211) had at least one NSI. Most NSIs had been reported in the emergency department (33.5%). Most participants mentioned the injection syringe needles as the main cause of their injuries (71.1% of all NSIs). Among NSIs, those caused by insulin syringe needles (6.2%) were the second cause. In this study, females had NSIs more than males. There was a statistically significant relationship between sex and the rate of NSIs (P < 0.05). Conclusions:Considering the high rate of occupational injuries, further preventive measures should be implemented to prevent these injuries from occurring. Providing initial and continuing training for employees is very important. Directing special attention to emergency department employees may be effective in reducing occupational injuries.