Chikungunya is a viral disease transmitted by a mosquito of the genus Aedes. It is currently epidemic on Reunion Island, in the Indian Ocean. It is essentially characterized by an influenza syndrome but associated with polyarthralgia and an eruption. The disabling and chronic nature of the arthralgia is the most remarkable clinical aspect of chikungunya infection. Severe and unusual forms have appeared, not previously described in the literature. These forms must be studied to determine whether there is a direct relation between the chikungunya virus and the severity factors. Treatment is solely symptomatic, combining analgesic and/or antiinflammatory agents. There is no vaccine. The epidemic is not limited to Reunion: cases of chikungunya have also been reported in neighboring islands (Maurice, Seychelles, and Madagascar). Travelers planning to visit the region should be counseled.