The core concept of plagiarism is defined as the use of other people's ideas or words without proper acknowledgement. Herein, we used a questionnaire to assess the knowledge of students of Tehran University of Medical Sciences (TUMS) regarding plagiarism and copyright infringement. The questionnaire comprised 8 questions. The first six questions of the questionnaire were translations of exercises of a book about academic writing and were concerning plagiarism in preparing articles. Questions number 7 and 8 (which were concerning plagiarism in preparing Microsoft PowerPoint slideshows and copyright infringement, respectively) were developed by the authors of the present study. The validity of the questionnaire was approved by five experts in the field of epidemiology and biostatistics. A pilot study consisting of a test and retest was carried to assess the reliability of the questionnaire. The sampling method was stratified random sampling, and the questionnaire was handed out to 74 interns of TUMS during July and August 2011. 14.9% of the students correctly answered the first six questions. 44.6% of the students were adequately familiar with proper referencing in Microsoft PowerPoint slideshows. 16.2% of the students understood what constitutes copyright infringement. The number of correctly answered questions by the students was directly proportionate to the number of their published articles. Knowledge of students of TUMS regarding plagiarism and copyright infringement is quite poor. Courses with specific focus on plagiarism and copyright infringement might help in this regard.