A breeding population of Nysius inconspicuus Distant., a pest of sunflower, was recorded for the first time in Pakistan. Duration of its growth stages, population build up during May and June and economic losses in sunflower were studied at National Agricultural Research Centre, Islamabad, during spring 1992. The development of N. inconspicuus Distant. was studied on sunflower florets and heads at an average temperature of 30.65℃ under laboratory conditions. Although nymphs did not survive on florets, their survival on sunflower heads was 60% in the first 20 days of development. The insect laid 12 eggs per female in captivity. The average incubation period and the nymphal duration was 5 and 20 days, respectively. The adults lived for 15 days. Thus the total life-span was 40 days. The pest appeared at seed formation stage and reached up to 58 individuals per sunflower head during the season. In a pot experiment 50 or more bugs per head caused about 26% losses in yield and 2% in oil content.