Introduction: A dengue outbreak was observed in Réunion in 2018, following low-level viral circulation in 2017. A surveillance system for hospitalized dengue cases was established. The objectives of this study are to describe the characteristics of hospitalized cases, to assess the completeness of this surveillance, and to evaluate the severity of the outbreak. Materials and Methods: The characteristics of cases hospitalized for more than 24 hours between April 2017 and December 2018 were described. The completeness of surveillance was assessed for the period from April 2017 to June 2018 using the capture-recapture method, based on data from the Hospital Information Systems Program (PMSI) and surveillance by Santé publique France - Indian Ocean. Results: Between April 2017 and December 2018, 168 hospitalized cases were identified by Santé publique France - Indian Ocean, representing 2% of confirmed or probable cases reported during the same period. Twenty-eight cases (18%) were severe, and 112 (70%) presented at least one warning sign. Five patients (3%) died. This surveillance made it possible to describe the trend in the number of hospitalized cases and to characterize the severity of these cases. However, its completeness was estimated at 50% between April 2017 and June 2018. Conclusion: The percentages of hospitalized cases and severe cases among these cases are lower than those described during the most recent epidemics in French Guiana and New Caledonia. Monitoring the severity of the epidemic was possible thanks to this surveillance. However, potential improvements are being considered regarding the methods of this surveillance.