Islam in Sri Lanka is practiced by a group of minorities who make up 9.72% of the population of Sri Lanka. 1,967,227 persons adhering Islam as per the census of 2012(There is 57227 reverts/converts not included in the latest census as Muslims)
With the arrival of Arab traders in the 8th century, Islam began to flourish in Sri Lanka. The first people to profess the Islamic faith were Arab merchants and their native wives, whom they married after converting to Islam.

http://en.wikipedia.org/wiki/Islam_in_Sri_Lanka