Mosquitoes belonging to the Culex pipiens complex were collected from several localities in Thailand and identified by using D/V ratios of male terminalia. Most of the mosquitoes were Cx. quinquefasciatus, having D/V ratios between 0.1-0.6, mean 0.35 ± 0.07. Among the mosquitoes from Klong Tauy, Phuket and Chiang Mai, 9/262 had D/V ratios of 0.7-0.9, which may be extreme variations of Cx. quinquefasciatus or may be the variety pallens of Culex pipiens.