Studies of Patagonian toothfish size composition in fishing area 48.3 were made to determine size at maturity for male and female individuals.A considerable amount of original data indicated that male Patagonian toothfish attained maturity being of a smaller size than female individuals. Half the males became mature when 73-75 cm long, while females matured when 94-96 cm long. Toothfish maturity ogive was drawn and compared with size composition in catches of recent years to show that currently long-line fishery has been taking large amounts of immature and newly matured fish < 90 cm long. Obviously large amounts of immature Patagonian toothfish in catches negatively affected the population status in this most productive and traditional fishing area. It is suggested that conservation measures, namely introduction of the minimum toothfish size for long-line catches could considerably reduce negative impacts of overfishing.