During the outbreak of Chikungunya (CHIK) that affected the Reunion Island in 2005/2006, the neonatal forms of infections acquired by mother-to-child transmission (MTCT) during childbirth, were reported in 50% of viremic mothers and associated with high neonate morbidity. MTCT occurred only when the mother was viremic at the time of delivery. The viremic period begins 2 days before the onset of symptoms and lasts for six days following the first symptoms. In infected neonates contaminated during labor, symptoms appeared after a median incubation period of 4 days. All neonate CHIK cases were symptomatic and the rate of severe forms was about 50%; these severe forms were primarily due to damages to the central nervous system, often leaving permanent damage (seizures, cerebral palsy).