The extensive vaccination efforts carried out by most countries in the Americas have succeeded in controlling the circulation of the endemic measles virus. To date, French Guiana remains the only territory in South America "outside" the regional measles elimination plan promoted by the World Health Organization. In January 2003, following the occurrence of a suspected case of measles at the border between French Guiana and Brazil, the Pan American Health Organization (PAHO) asked Guyana’s health authorities to quickly determine whether the measles virus was circulating in Guyana and to assess the remaining efforts required by vaccination services to achieve measles vaccination coverage of at least 95% across the entire territory. Furthermore, the occurrence of two successive pertussis epidemics in March and December 2001 and the finding of very inadequate vaccination coverage with four doses of pertussis vaccine throughout the territory led to an evaluation of pertussis vaccination activities as well. A survey, whose methodology was adapted from the Lot Quality Assurance Sampling method by PAHO, was conducted in April 2003 in 43 sectors across French Guiana. In each sector, 20 households with at least one child aged 2 to 6 years were visited. A sector was considered under-vaccinated when two or more children were found to be unvaccinated against measles or pertussis. This study was supplemented by active door-to-door case-finding for measles. The evaluation of vaccination activities identified 27 out of 36 valid sectors (20 children aged 2–6 years or more than one unvaccinated child) as having insufficient measles vaccination coverage and 39 out of 43 sectors as having insufficient pertussis vaccination coverage. Active case finding detected no suspected cases either within the family or among the contacts of the interviewed individuals. The results of this survey thus showed that most health services are unable to maintain sufficient vaccination coverage to interrupt the circulation of the measles virus. Similarly, vaccination with four doses of pertussis remains very inadequate despite the vaccination campaigns conducted in 2002. Consequently, the risk of outbreaks, which are often fatal for infants, remains high in French Guiana. This alarming situation requires that a genuine EPI covering all vaccines on the schedule and providing for more active vaccination strategies be implemented in the near future in this department. This program must integrate the regional program led by PAHO in the English-speaking Caribbean and Suriname.