Delphi technique is an approach used tu gain consensus among a panel of experts. This is normally achieved through a series of rounds where information is fed back to panel members using questionnaires. It has been used extensively within social science research and is being increasingly employed by nurse researchers. This popularity has meant that the technique has been adapted in various ways and there is the possibility that the rigour associated with the original format has been threatened. This signals the need for a critical review of the Delphi as a robust and systematic approach to data collection. While there is a great volume of literature surrounding the `Delphi', there is a dearth of papers critically analysing the technique. This paper aims: to examine critically the Delphi technique from a range of perspectives. Discussion will focus on problems of definition and the advantages and disadvantages and the techniques' application in nursing. The critique will be structured through an analysis of the key aspects of the Delphi process. These key aspects include analysis of sampling, anonymity. use of experts. rounds and application. The critical analysis highlights the increasing popularity of the Delphi and the modifications to the process which may cause methodological problems. Ultimately, the Delphi has much to offer in terms of gaining consensus from a wide range of individuals on specific topics. (C) 2001 Elsevier Science Ltd. All rights reserved.