There has been a substantial decline in the use of female sex hormone replacement therapy (HRT) in the United Kingdom, particularly by post-menopausal women, since around 2000-2001. Given what is known of the risk of breast cancer in women receiving HRT, the decline in use should have resulted in a decrease in risk, and incidence rates about 14% lower than expected were predicted for the age group 50-59 in 2005. There has been a recent slowing and reversal of the increasing trends in incidence of breast cancer in the age group 45-64. This is most marked at ages 50-59, where rates since 1999 have been decreasing at 0.8% a year, following a long period of sustained increase. It seems probable that these two events are causally related.