Natural cycle IVF (NIVF) arose from a wish to understand intrafollicular events in couples with unexplained infertility. Single follicle aspiration required unusual technical skill and a precise understanding of the endocrinology in the ostensibly normal cycle. The application of NIVF to all candidates for assisted conception resulted in a low delivery rate. However once data had accumulated it became apparent that age, follicular phase FSH concentrations and other endocrine abnormalities were associated with high failure rates. The concept of using NIVF as a preliminary screening cycle arose. By early elimination of some candidates and selective inclusion of others a highly cost effective regime can be developed. Taking delivery rates into account the cost per maternity is only half that of stimulated IVF. Using clear cut algorithms for the investigation of different categories of infertility the place of NIVF can be defined. Current UK discussions relate to exclusions from access to IVF. Biological exclusions such as age could further enhance the cost effectiveness of NIVF. When NIVF can contribute to at least 50% of cycles in an assisted conception programme it has the potential to have a major economic impact.