This article provides evidence on the effectiveness of voluntary positive action in addressing inequality between female and male careers. The setting is UK medical schools where two natural experiments are exploited. The first is the introduction of the Athena SWAN charter in 2005, whereby 12 UK universities signed up to the principles of the charter. The second is the announcement in 2011 by the National Institute for Health Research to only shortlist medical schools with a ‘silver’ Athena SWAN award for certain research grants. This second change potentially impacts schools that are further away from silver status more than those that were already close in 2011. While there is a marked improvement of women succeeding in medical schools between 2004 and 2013, early Athena SWAN adopters have not increased female participation by more than other schools whose institution signed up later. In addition, tying funding to Athena SWAN silver status has yet to have an impact on female careers, although medical schools have invested in efforts to achieve silver status. Together, these results emphasize the challenges associated with addressing gender equality through voluntary self‐regulation.