The dispersal of Culex quinquefasciatus was studied near Norco, California in a periurban situation of southern California. Concurrent studies indicated that host-seeking females were most active up to one hour after sunset. A mark-release-recapture technique was used to document a mean distance traveled of 0.91 km in 12 hr (the first flight period) and a cumulative distance of 1.27 km after 36 hr (following the second flight period). Nearly 0.32% of 47,750 marked females were recaptured. A majority of the population moved with the prevailing wind. Unmarked females were captured at all trapping locations in the study.