How often did a second stroke occur after a first?

In South London, among 5,509 people whose first-ever stroke was recorded between 1995 and 2019, the chance of having a second stroke within five years was about one in ten (9.6% at 5 years). The estimate comes from the South London Stroke Register, which followed people over many years. To estimate recurrence, the researchers used a cumulative incidence function—a calculation that counts how many people in the original group would have a second stroke by a given time while allowing for the fact that some die first. A death is treated as a competing event, meaning someone who dies is no longer able to have a second stroke.

Death matters here because it is common: during 34,874 person-years of follow-up, 2,666 people (48.4%) died, while 680 (12.3%) had a recurrence. If researchers simply ignored deaths, the estimate of recurrence could be biased. Treating death as a competing event means that people who die are counted as no longer at risk of a second stroke, which gives a more accurate population-level estimate. The 12.3% figure is the raw recurrence count across all observed follow-up, not the same as the five-year cumulative probability of 9.6%.

The cumulative recurrence risk was 14.1% at 15 years and 15.2% at 25 years, so the risk continued to accumulate slowly after the first five years. These percentages describe the whole register population; an individual's own chance may be higher or lower.

The register also showed some characteristics associated with a second stroke. After an ischemic stroke, hypertension was associated with higher recurrence risk. After a hemorrhagic stroke, diabetes was associated with higher recurrence risk. These are associations from the register analysis, not proof that these conditions directly caused the second stroke.

Overall, stroke recurrence risk remains substantial after both ischemic and hemorrhagic stroke. Accounting for death as a competing event provides more accurate estimates and highlights the importance of demographic and clinical factors in recurrence prevention. These findings come from the South London Stroke Register, covering people with first-ever stroke between 1995 and 2019. For ischemic stroke, earlier cohorts had higher recurrence risks, so the average may not apply equally to later periods or other locations. The results are population-level descriptions, not personal predictions for any one patient.