Gonad development, seasonal changes in gonad activity, and size at maturity were investigated in female and male yellowtail kingfish (Seriola lalandi;Carangidae) collected from New South Wales, Australia between August 1995 and June 1996. Kingfish displayed peak gonad activity in December suggesting a summer spawning period. Males matured at smaller sizes than females. Females first matured at 698 mm fork length (FL) and 3+ years, but 50% maturity was not attained until 834 mm FL. The smallest recorded mature male was 360 mm FL and the estimated size at which 50% of males were mature was 470 mm FL (0+ years). Many female fish are harvested prior to first reproduction, but the impact of this on the stock remains unclear.