The seasonal appearance of Aedes albopictus was observed from January 1978 to April 1979 in Naha City, Okinawa prefecture. In Okinawajima, all immature stages and adults were collected every month of the year. The highest density of immature stages was observed in July and their numbers then sharply decreasing through late August. The number of immatures increased again in September and then decreased gradually from October to February. The females fed readily on humans and oviposited on warm days in winter, and adult emergence occurred even in the coldest month.