In 2001, a vaccination campaign against yellow fever was carried out in Abidjan, Cote d'Ivoire. During the campaign and 4 weeks after an active surveillance system for adverse events following immunization (AEFI) was set up. More then 2.6 million doses were administered and 87 AEFI were notified. Eight suspected YF cases were reported after vaccination and considered as AEFI. However, none had IgM for YF and all recovered without sequels. This surveillance system provided reassuring data about the safety of the YF vaccine and proved that it is feasible to set up an active surveillance system during a mass campaign.