The first wave of the 2009 influenza A(H1N1) epidemic occurred on Réunion Island during the southern winter, as in most countries in the Southern Hemisphere. This episode, which lasted 9 weeks, resulted in an incidence rate of 8.26%, with an estimated total of nearly 67,000 people seeking medical care between July 20 and September 20, 2009. The enhanced surveillance system, based on multiple data sources, proved useful both for tracking the dynamics of the epidemic on Réunion Island and for quantifying its impact. (R.A.)