Objective: To assess the effectiveness of emergency single-dose levonorgestrel contraception in preventing unintended pregnancies among woman who visited the emergency department (ED) due to sexual assault (SA). Methods: We conducted a retrospective chart review in a university hospital in South Korea. Cases from November 10, 2006 to November 9, 2009 were enrolled. Information from the initial visit to the ED and subsequent follow-up visits to the gynecology outpatient clinic was collected. Results: In total, 1,179 women visited the ED due to SA. Among them, 416 patients had a gynecological examination and 302 patients who received emergency contraception (EC) (1.5 mg single-dose levonorgestrel) at the ED due to SA were enrolled. Ten patients did not return for follow-up examinations. In follow-up visits at the outpatient clinic, two pregnancies were confirmed, which showed the failure rate of the EC to be 0.68%. Conclusion: Single-dose levonorgestrel EC is extremely effective at preventing pregnancy among victims of SA.