As part of a learning exercise to assess the efficiency of oocyte utilization after controlled ovarian stimulation, we compared historical data from the publications of Steptoe and Edwards describing their early experiences in Oldham and at Bourn Hall with retrospective data from IVF and ICSI cycles carried out at Bourn Hall Clinic during the year 2000. For the purpose of analysing the more recent data, patients were subdivided into groups by age (< or = 37 years and > or = 38 years) and by oocyte yield (low, intermediate and high). In patients less than 38 years of age, live birth rates were equivalent in each group, irrespective of the number of oocytes retrieved. Patients who yielded low numbers of oocytes (1-5) utilized an average of 9.6 oocytes per live birth, compared with 25.1 and 51.5 in those who yielded intermediate (6-16) and high (16+) numbers of oocytes. The comparison with historical data suggests that the 'efficiency' of oocyte utilization has not improved significantly since the early 1980s, despite 25 years' experience of controlled ovarian stimulation for IVF treatment.