Low-dose transdermal oestrogen patches do not appear to raise the risk of stroke. However, high-dose patches, oral HRT using oestrogen alone or combined with a progestagen, are associated with an increased risk. A total of 15,710 cases of stroke were identified, from a cohort of nearly 900,000 women aged 50-79, on the General Practice Research Database; giving an incidence of 2.85 per 1,000 woman-years. The average age at stroke was 70 years. Four matched controls were selected for each case. [With external links to current evidence and summaries]