Understanding the ecology and behavior of different mosquito species is essential for identifying their role in disease transmission cycles and human risk. Two species of Culex mosquitoes in the Northeastern United States have been implicated in enzootic transmission of West Nile virus. Despite the difficulty of differentiating these two species as adults, many public health workers and vector biologists separate them based on morphology. We evaluated the reliability of eight morphological characters for accurate adult identification of these species by comparing morphology with DNA sequence confirmations for Cx. pipiens and Cx. restuans collected in New York State. Mosquitoes were identified correctly as Cx. pipiens and Cx. restuans as having at least 7 of 8 putative morphological traits only 25% and 4% of the time, respectively. For Cx. pipiens, integument color and abdominal band width and arrangement were the most reliable morphological traits. For Cx. restuans, abdominal band color was most reliable. Our study clearly indicates the lack of reliability for morphological identification of Cx. pipiens and Cx. restuans. In order to fully understand the respective roles of Culex species in the epidemiology of WNV and transmission of other pathogens, more effort should be placed on accurate identification of these important vector species.