Background: Plagiarism is considered as serious research misconduct, together with data fabrication and falsification. However, little is known about biomedical researchers' views on plagiarism. Moreover, it has been arguedbased on limited empirical evidencethat perceptions of plagiarism depend on cultural and other determinants. The authors explored, by means of an online survey among 46 reputable universities in Europe and China, how plagiarism is perceived by biomedical researchers in both regions. Methods: We collected work e-mail addresses of biomedical researchers identified through the websites of 13 reputable universities in Europe and 33 reputable universities in China and invited them to participate in an online anonymous survey. Our questionnaire was designed to assess respondents' views about plagiarism by asking whether they considered specific practices as plagiarism. We analyzed if respondents in China and Europe responded differently, using logistic regression analysis with adjustments for demographic and other relevant factors. Results: The authors obtained valid responses from 204 researchers based in China (response rate 2.1%) and 826 researchers based in Europe (response rate 5.6%). Copying text from someone else's publication without crediting the source, using idea(s) from someone else's publication without crediting the source and republishing one's own work in another language without crediting the source were considered as plagiarism by 98, 67 and 64%, respectively. About one-third of the respondents reported to have been unsure whether they had been plagiarizing. Overall, the pattern of responses was similar among respondents based in Europe and China. Nevertheless, for some items significant differences did occur in disadvantage of Chinese respondents. Conclusions: Findings indicate that nearly all biomedical researchers understand (and disapprove of) the most obvious forms of plagiarism, but uncertainties and doubts were apparent for many aspects. And the minority of researchers who did not recognize some types of plagiarism as plagiarism was larger among China-based respondents than among Europe-based respondents. The authors conclude that biomedical researchers need clearer working definitions of plagiarism in order to deal with grey zones.