Few data exist on the health status and heathcare utilization of the undocumented migrants in France. Data are particularly scarce in French overseas territories where this population is numerous. We aimed to describe the characteristics of undocumented patients who use the emergency department of Saint-Laurent du Maroni Hospital(SLMH) in French Guiana, and to identify factors associated with their subsequent hospitalization. In a random sample of 177 patients, we used logistic regression models to test the mediational role of health-care system utilization and medical characteristics at admission in the association between residency status and hospitalization.More than a quarter of patients (27.7 %) were undocumented migrants, who were subsequently hospitalized more often than the others [OR 3.11, 95 % CI (1.32–7.34)]. More-severe symptoms at admission, a poorer access to health insurance, a greater distance between their home and SLMH, and poorer French language skills partially explained this higher hospitalization rate. Despite the fact that France has instituted a specific insurance program for the undocumented, an increasing number of barriers to accessing health care is being reported for these people. Our results suggest that these obstacles have some impacts in the utilization of hospital care.