Introduction and Objectives: The first locally acquired cases of chikungunya (Chik) in the Americas were reported in Saint Martin in October 2013. The outbreak was declared on December 5, 2013. These cases occurred amid a dengue outbreak that had been ongoing for a year. The vector for these two arboviral diseases in Saint Martin (Aedes aegypti) differs from that in Réunion. To characterize hospitalized cases, active surveillance was implemented. Materials and Methods: Since the start of the epidemic, a data collection form has been completed for all cases of Chik—whether confirmed (PCR+) or probable (IgM+)— and hospitalized for more than 24 hours. Each case was classified as a maternal-neonatal form (non-severe or severe) if the newborn was < 10 days old, or as a common, unusual non-severe, or severe form (organ failure) if the age was > 10 days. Results: As of March 14, 2014, 27 cases had been hospitalized. The average incidence was 7.3 per 10,000 inhabitants, higher at the extremes of age (24.1 among those < 5 years and 86.4 among those > 75 years). The following were observed: 1 non-severe maternal-neonatal form, 16 common forms (59%), 7 unusual forms (26%), and 3 severe forms (11%). Among the unusual forms: 4 cases with seizures, including 3 children and 1 adult without associated encephalitis, 1 hyperalgesic syndrome, 1 vaso-occlusive crisis in a patient with sickle cell disease, and a pure nephrotic syndrome with signs of autoimmunity suggestive of lupus (spontaneous remission). The latter occurred 1 month after dengue. The 3 severe forms affected adults > 65 years of age with cardiovascular comorbidities (2 cases of respiratory distress, including 1 with gastric necrosis, and 1 massive ischemic stroke with limb ischemia). All 3 patients died. Conclusion: These results confirm the existence of unusual non-severe and severe forms of Chikungunya. Continued surveillance will allow for further data collection. (R.A.)