The authors conducted a nationwide cohort study to evaluate the association 
between postmenopausal hormone therapy and meningioma incidence in Finland. All 
women who had used hormone therapy at least for 6 months at the age of 50 years 
or older during 1994-2009 were included. Women who had used postmenopausal 
hormone therapy were identified from the medical reimbursement register of the 
Social Insurance Institution (131,480 estradiol users and 131,248 
estradiol-progestin users), and meningioma cases were identified from the 
Finnish Cancer Registry. During the average 9 years of follow-up, 289 estradiol 
users and 196 estradiol-progestin users were diagnosed with meningioma. Ever use 
of estradiol-only therapy was associated with an increased risk of meningioma 
(standardized incidence ratio = 1.29, 95% confidence interval: 1.15, 1.44). 
Among women who had been using estradiol-only therapy for at least 3 years, the 
incidence of meningioma was 1.40-fold higher (95% confidence interval: 1.18, 
1.64; P < 0.001) than in the background population. In contrast, this risk was 
not increased in users of combination therapy (standardized incidence ratio = 
0.93, 95% confidence interval: 0.80, 1.06). There was no difference in risk 
between continuous and sequential use of hormone therapy. Estradiol-only therapy 
was accompanied with a slightly increased risk of meningioma.