Objectives: The objective of this research is to analyse the evolution and nature of published empirical research in the fields of medical ethics and bioethics.Design: Retrospective quantitative study of nine peer reviewed journals in the field of bioethics and medical ethics .Results: In total, 4029 articles published between 1990 and 2003 were retrieved from the journals studied. Over this period, 435 studies used an empirical design. The highest percentage of empirical research articles appeared in Nursing Ethics , followed by the (...) Journal of Medical Ethics and the Journal of Clinical Ethics . These three journals account for 84.1% of all empirical research in bioethics published in this period. The results of the χ2 test for two independent samples for the entire dataset indicate that the period 1997–2003 presented a higher number of empirical studies than did the period 1990–1996 . This increase is statistically significant . Most empirical studies employed a quantitative paradigm . The main topic of research was prolongation of life and euthanasia .Conclusions: We conclude that the proportion of empirical research in the nine journals increased steadily from 5.4% in 1990 to 15.4% in 2003. It is likely that the importance of empirical methods in medical ethics and bioethics will continue to increase. (shrink)