The authors of a letter in Emerging Infectious Diseases (I) incorrectly stated that the first Zika virus (ZIKV) outbreak outside Africa and Asia was retrospectively identified from serum samples initially diagnosed as dengue virus (DENV) in Yap, Federated States of Micronesia. However, the outbreak was first identified by the Yap State Department of Health Services, and an investigation was initiated to determine the cause. Although dengue was initially considered, clinicians in Yap believed the clinical symptoms did not match dengue. Assistance was sought from the US Centers for Disease Control and Prevention (CDC) and the World Health Organization to strengthen the investigation and provide confirmatory testing. Serum samples were sent to the CDC's Arboviral Diseases Diagnostic Laboratory, where testing confirmed ZIKV as the cause. This discovery was the result of an active, coordinated investigation by the Yap State Department of Health Services with support from international partners, not retrospective testing of samples initially diagnosed as DENV. The authors apologize for the inaccuracy and encourage readers to consult the articles by Lanciotti et al. and Duffy et al. for a complete description of the clinical and laboratory investigations. Without data and laboratory protocols from the 2007 outbreak, identifying ZIKV as the cause of the 2013 outbreak in French Polynesia would have been delayed.The authors of a letter in Emerging Infectious Diseases (I) incorrectly stated that the first Zika virus (ZIKV) outbreak outside Africa and Asia was retrospectively identified from serum samples initially diagnosed as dengue virus (DENV) in Yap, Federated States of Micronesia. However, the outbreak was first identified by the Yap State Department of Health Services, and an investigation was initiated to determine the cause. Although dengue was initially considered, clinicians in Yap believed the clinical symptoms did not match dengue. Assistance was sought from the US Centers for Disease Control and Prevention (CDC) and the World Health Organization to strengthen the investigation and provide confirmatory testing. Serum samples were sent to the CDC's Arboviral Diseases Diagnostic Laboratory, where testing confirmed ZIKV as the cause. This discovery was the result of an active, coordinated investigation by the Yap State Department of Health Services with support from international partners, not retrospective testing of samples initially diagnosed as DENV. The authors apologize for the inaccuracy and encourage readers to consult the articles by Lanciotti et al. and Duffy et al. for a complete description of the clinical and laboratory investigations. Without data and laboratory protocols from the 2007 outbreak, identifying ZIKV as the cause of the 2013 outbreak in French Polynesia would have been delayed.