BACKGROUND: The Women's Health Initiative (WHI) and other clinical trials indicate that significant health risks are associated with combination hormone use. Less is known about the effect of hormone therapy on health-related quality of life. METHODS: The WHI randomly assigned 16,608 postmenopausal women 50 to 79 years of age (mean, 63) with an intact uterus at base line to estrogen plus progestin (0.625 mg of conjugated equine estrogen plus 2.5 mg of medroxyprogesterone acetate, in 8506 women) or placebo (in 8102 women). Quality-of-life measures were collected at base line and at one year in all women and at three years in a subgroup of 1511 women. RESULTS: Randomization to estrogen plus progestin resulted in no significant effects on general health, vitality, mental health, depressive symptoms, or sexual satisfaction. The use of estrogen plus progestin was associated with a statistically significant but small and not clinically meaningful benefit in terms of sleep disturbance, physical functioning, and bodily pain after one year (the mean benefit in terms of sleep disturbance was 0.4 point on a 20-point scale, in terms of physical functioning 0.8 point on a 100-point scale, and in terms of pain 1.9 points on a 100-point scale). At three years, there were no significant benefits in terms of any quality-of-life outcomes. Among women 50 to 54 years of age with moderate-to-severe vasomotor symptoms at base line, estrogen and progestin improved vasomotor symptoms and resulted in a small benefit in terms of sleep disturbance but no benefit in terms of the other quality-of-life outcomes. CONCLUSIONS: In this trial in postmenopausal women, estrogen plus progestin did not have a clinically meaningful effect on health-related quality of life.