Abstract.-Data on size, age, and fecundity of mature pink salmon (Oncorhynchus gorbuscha) were collected during 1973-84. Most salmon matured when 2 years old and the males were significantly longer than females in all three lakes. Mean lengths (mm) of males and females were: Lake Superior- 387 and 379, Lake Huron- 468 and 436, and Lake Michigan- 482 and 443. Salmon that matured in 3 years were found only in Lake Superior tributaries and again males were significantly longer than females (487 versus 467). Until the middle 1970's all pink salmon were assumed to mature when they were 2 years old but a mature 3-year-old salmon was found in 1976 and 3-year-old salmon have since become common. Mean fecundity of 127 pink salmon from lakes Superior and Huron was 1,030 eggs. Fecundity of 2-and 3-year-old salmon was similar.