Use of hormone replacement therapy (HRT) has been hypothesized to affect survival of epithelial ovarian cancer (EOC). We studied 5-year survival in patients with invasive EOC and borderline ovarian tumors (BOT) according to HRT use before and after diagnosis in a prospective nation-wide cohort study of 799 women diagnosed with EOC (n 5 649) and BOT (n 5 150) aged 50-74 years in 1993-1995 in Sweden. Cox regression was used to obtain multivariate age-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs). Multivariate models included indicator variables for age, tumor stage, grade and histological subtype. After 5 years of follow-up, 45% of the patients with EOC and 93% of the patients with BOT were alive. For women with BOT there were no associations between HRT-use pre-or postdiagnosis and survival. There was no overall difference in 5-year EOC survival according to use HRT before diagnosis (multivariate HR 5 0.83, 95% CI 5 0.65-1.08), except for serous EOC (HR 5 0.69, 95% CI 5 0.48-0.98). Analyses of different HRT preparations, duration and recency of use did not reveal any variations in pattern of survival. We observed a better survival for EOC-patients who used HRT after diagnosis (multivariate HR 5 0.57, 95% CI 5 0.42-0.78). We conclude that HRT-use prior to diagnosis of EOC does not affect 5-year survival, except for a possible survival advantage in serous EOC. Women using HRT after diagnosis had a better survival than women with no use, but we cannot rule out that this latter finding may reflect a subtle selection process. ' 2006 Wiley-Liss, Inc.Key words: ovarian cancer; hormonal replacement therapy; survival; mortality; Sweden Hormonal factors are believed to be of fundamental importance in the etiology of ovarian cancer, the 6th most frequent type of female cancer in the world. 1 Ovarian cancer is usually associated with a rather poor prognosis, with overall 5-year survival rates commonly less than 40%. 2 In recent decades in Sweden, HRT has been widely used for relief of climacteric symptoms and to prevent osteoporosis. Progestins without estrogens are mainly used for the treatment of climacteric bleeding irregularities, and for the alleviation of symptoms related to benign appearing ovarian cysts. Estriol can be bought over the counter, and is mostly used for symptomatic treatment of vaginal or urethral atrophy among elderly women. 3,4 While effectively relieving women of climacteric symptoms, use of menopausal hormones has been shown to increase risks of different types of cancer. For breast cancer, there is growing evidence that cyclically combined estrogen-progestin therapy increase risk even more than estrogens alone. 5-8 For endometrial cancer estrogens alone increase risk substantially, as do use of cyclically combined estrogen-progestins. [8][9][10] For epithelial ovarian cancer (EOC) estrogen without progestins, or cyclically combined estrogen-progestins therapy increases risk. 8,11,12 There are few studies on the effects of regimens of estrogens continuously combined to progestins: t...