The most common definition of pre-eclampsia involves hypertension and proteinuria. This has changed little in over a hundred years despite advances in understanding the underlying pathological process. However, a number of variations in definition exist, and this paper demonstrates a lack of consistency in research articles in defining pre-eclampsia. A quarter of papers omit description, and many authors choose their own interpretation of the standard classification. Editors and reviewers should ensure that papers include a clear description of the definition used and an adequate description of the population studied to allow meaningful interpretation of research findings.