On November 4, 2010, a case of wild poliovirus type 1 (WPV1) was confirmed in a resident of the port city, Pointe Noire, the first WPV case in Republic of the Congo (ROC) in 10 years. The WPV1 isolate from this resident was genetically most closely related to WPV1 isolated in Angola in 2010. Subsequent investigation, including active case finding, revealed increased acute flaccid paralysis (AFP) hospital admissions beginning in September. Weekly admissions rose from approximately 10 AFP patients in early October to approximately 80 by the end of October and November. With response immunization activities, weekly AFP admissions fell to fewer than five by the end of December. A provisional total of 554 AFP cases were identified nationally, with paralysis onset from September 20, 2010, to February 27, 2011; 374 (68%) of the AFP cases were among males. Overall, 465 (84%) AFP cases were among residents of the neighboring departments of Kouilou and Pointe Noire, where the outbreak apparently began and where approximately 21% of ROC's 4.2 million persons reside. The case-fatality rate (CFR) in Kouilou and Pointe Noire was 40% (187 deaths of 465 cases), compared with 11% (10 of 89) elsewhere in ROC. Additionally, the median age of patients with AFP in Kouilou and Pointe Noire was 20 years (range: 0-63 years), compared with 7.5 years (range: 1-68 years) elsewhere in ROC.