Health risk assessment is important in the safe deployment of workers to tropical areas. We monitored dengue incidence in 204 of 222 North American relief workers visiting Puerto Rico after Hurricane Georges and during a dengue epidemic in 1998. We recorded information regarding participants' living conditions and any illness they experienced from arrival to 2 weeks after their departure. Virus isolation, polymerase chain reaction, and serological tests for anti-dengue immunoglobulin (Ig) M and IgG antibodies were used to diagnose dengue infection by means of departure and follow-up serum specimens. Among respondents, 82% (164 of 199) reported mosquito bites, 97% (156 of 161) reported having insect repellent available, and 41% (79 of 195) reported using repellent every day. Twelve participants reported a mild denguelike illness. No participants had laboratory evidence of dengue infection after 1.8 person-years of assessable exposure to areas with dengue transmission (upper 95% confidence limit of 1.67 cases per person-year). The risk of acquiring dengue among relief workers in this study appears low, possibly as a result of protective factors. Travelers to dengue-endemic areas should continue to be advised to protect themselves against mosquito bites.