In the 1990s, two randomised clinical trials started in Scandinavia addressing whether hormone replacement therapy (HRT) is safe for women with previous breast cancer. We report the findings of the safety analysis in HABITS (hormonal replacement therapy after breast cancer--is it safe?), an open randomised clinical trial with allocation to either HRT or best treatment without hormones. The main endpoint was any new breast cancer event. All analyses were done according to intention-to-treat. Until September, 2003, 434 women were randomised; 345 had at least one follow-up report. After a median follow-up of 2.1 years, 26 women in the HRT group and seven in the non-HRT group had a new breast-cancer event. All women with an event in the HRT group and two of those in the non-HRT group were exposed to HRT and most women had their event when on treatment. We decided that these findings indicated an unacceptable risk for women exposed to HRT in the HABITS trial, and the trial was terminated on Dec 17, 2003.