In 2009, the region of Dakar (Senegal) experienced a major measles epidemic, in the context of the failure of the immunization program. The objective of this study was to examine the epidemic and the effectiveness of the response. A cross-sectional epidemiological study of all cases of measles confirmed by laboratory tests or epidemiological linkage was conducted between June and December 2009. The study also assessed the effectiveness of the response. The results show that out of 767 confirmed cases, less than a third (30 %) were laboratory-confirmed, while the remaining cases were confirmed by epidemiological linkage with one or several other confirmed cases. The minimum age was 4 months and the maximum age was 35 years. Children under 5 accounted for 67.4 % of the total number of cases. The male population was more affected than the female population (52.2 %). Most of the cases of were not vaccinated (88.5 %). The southern district had the highest incidence of measles, with more than 68 cases per 100,000 inhabitants. The vaccination coverage rate over the last 3 years was found to be satisfactory (average rate: 82.2 %). The response campaign resulted in the vaccination of 54,793 children aged 9 to 59 months (55.9%) distributed throughout the high-risk areas with low immunization coverage. No deaths were reported. The results suggest that it is important i) to continue to promote measles vaccination; ii) to combine routine vaccinations with supplements (for example vitamin A); iii) to introduce national vaccination campaigns targeting specific groups (new army recruits, students, refugees, etc.); and iv) to introduce a second dose of vaccine to ensure that the children who did not receive the first vaccine are covered and to address primary vaccine failures among those who were vaccinated.