Background The field of bioethics is constantly evolving. To investigate trends in the field of bioethics, we conducted a quantitative analysis of the top-cited articles in bioethical journals over the past 40 years.

Methods Retrospective quantitative study of the 20 most cited bioethics articles published each year from 1975 to 2014 were conducted. Article samples were selected from a list of the most relevant 100 journals in the field of bioethics.

Results In total, 800 top-cited articles between 1975 and 2014 in the domain of bioethics were retrieved and analysed. More than half of them were composed by single authors, but multiauthorship became more prevalent with time. The majority (84.5%) of these highly cited articles originated from the USA (65.3%), UK or Canada, though the proportion of other countries increased in recent years. Almost half (44.6%) of the highly cited articles belonged to the subfield of clinical ethics, but other subfields such as research ethics, public health ethics and neuroethics became more prominent. Overall, the distribution of Thesaurus keywords and subfields became more diverse over time, and the number of journals publishing top-cited articles doubled. Furthermore, the empirical ethics approach increased over time in our sample of top-cited articles.

Conclusions In sum, the forefront of bioethics is getting more diversified, collaborative and international. The presumed ‘mainstream’ becomes less dominant over time, as more highly cited articles come from new subfields, discuss new topics, use more Bioethics Thesaurus keywords, more authors participate and more countries other than the USA contribute to bioethics journals.