Objective First, to estimate the preventive and the curative effects of postmenopausal hormone therapy (PHT) on menopausal symptoms, and secondly to estimate the sensitivity of a woman to identify the exposure to postmenopausal hormone therapy. Design Randomised and blinded trial Setting Postmenopausal Hormone Therapy Trial in Estonia (EPHT), 1999-2002 Participants 593 women who responded to the relevant questions both at the entry and one-year follow-up questionnaires in the blind sub-trial Intervention HT or placebo at entry in women with or without menopausal symptoms Results The participants were asked in the questionnaires the presence of the menopausal symptoms of sweating, hot flushes and sleeping disorders, and at one-year follow-up to identify the exposure (HT or placebo). The net curative effect of HT (the proportion of disappeared symptoms in symptomatic women in the HT arm (46.4%) minus the same proportion in the placebo arm (25.8%) was 20.6%. The net preventive effect of HT (the proportion of incident symptoms in asymptomatic women in the placebo arm, 44.4%, minus the same proportion in the HT arm, 14.3%) was 30.1%. At one-year follow-up 34.6% of the women in the HT arm made a right guess on their arm. The net sensitivity of guessing the HT (right guess on HT minus wrong guess on placebo) was 15.8%. Conclusions The true HT effect on menopausal symptoms was relatively small. The clinical practice may need to further consider the benefit harm ratio of PHT [ISRCTN35338757].