Objective: To examine the association between postmenopausal hormone therapy (HT) and Alzheimer's disease (AD). Methods: Medicine and Alzheimer's disease (MEDALZ) is a nested case-control study of the entire Finnish population with clinically verified AD from 2005 to 2011 and up to 4 matched controls per case. This study comprises 230,580 women (46,117 cases and 184,463 controls). Data on HT use from 1995 to 2011 was extracted from the national prescription register using following ATC codes: GO3C (estrogen), GO3D (progestogen) and GO3F (estrogen and progestogen in combination). Only systemic HT (oral or transdermal) was considered. Results: Use of systemic estrogen and progestogen was associated with an increased risk of AD, with ORs (95% CI) of 1.10 (1.06-1.12) and 1.13 (1.10-1.17) respectively, but use of systemic estrogen HT for >10 years (OR, 95% CI: 0.91, 0.84-0.99) was protective against AD. Long-term (>10 years) use of progestogen and combination HT was not related to AD risk (OR, 95% CI: 1.0, 0.90-1.2). Conclusion: Our findings do not suggest HT is an important determinant of AD risk. (C) 2017 Elsevier B.V. All rights reserved.