The incidence of strokes in a large area of the south of the capital fell by 39.5% between 1995 and 2010, from 247 per 100,000 population to 149.5.
Rates fell in men,women, white groups and those aged more than 45 - but not in those aged 15 to 44, or black groups.
Researchers from King's College, investigated data in the South London Stroke Register, covering more than 350,000 people.
Between January 1995 and December 2010, 4,245 patients with first-ever stroke were registered.
The average age of onset of stroke decreased from 71.7 years to 69.6.
There were significant increases in the proportion of 15-44-year-olds.
The proportion of black patients also increased during the study period.
The researchers, whose findings are published in the medical journal Stroke, say the ethnic disparities may be because of different heart risk factors.