Samples of cod were collected from fishing gears in the coastal areas of Newfoundland and Labrador and from research otter-trawlers on the neighbouring banks from 1947 to 1950. Collections for the most part were from early summer to early autumn. Ages were determined using otoliths. Calculations of growth were based on average lengths and weights of the different age-groups in the samples.The growth rates of cod from various parts of the area were found to differ widely. Labrador cod had the slowest growth rate, much slower than cod from other parts of the area. Cod from the east coast of Newfoundland and the northeastern part of the Grand Bank were also slow-growing. Cod from the southwestern part of the Grand Bank had the fastest growth rate. Though cod from St. Pierre Bank and southwestern Newfoundland were fast-growing, also, they exhibited a somewhat slower growth rate than those from the southwestern part of the Grand Bank. Cod from the west coast of Newfoundland grew faster than cod from the east coast, but slower than those from southwestern Newfoundland.Though differences in growth rate were small between the sexes, the females generally grew at a slightly faster rate.The influence of differences in temperature and in food supply on the growth of cod in the area is discussed.Comparable growth data for the area published by several investigators are discussed. It is suggested that differences in these data were the result of variation in sampling locality, different sampling gears, different combination of individual samples and differences in age estimation.Both the size and age at which all fish were sexually mature varied throughout the area of investigation. Labrador cod matured at an earlier age and smaller size than cod from other parts of the area, whereas cod from the southwestern part of the Grand Bank generally matured at a later age and larger size than cod from other parts of the area. Cod from the east coast of Newfoundland, the northeastern part of the Grand Bank, St. Pierre Bank and the southwest and west coasts of Newfoundland were intermediate between cod from Labrador and the southwestern part of the Grand Bank in age and size at maturity, fish from the east coast generally maturing at an earlier age and smaller size than fish to the south on the Grand Bank and St. Pierre Bank and from the southwest and west coasts.The age, growth and sexual maturity relationships of cod from various parts of the area, when analyzed in the light of tagging experiments, meristic studies, parasite studies and hydrographic information, suggest the existence of at least four relatively distinct divisions in the cod population of the area, between which there is only limited intermingling. These are the Labrador, the Newfoundland east coast, the southern Grand Bank and the Newfoundland west coast divisions, with areas such as St. Pierre Bank and the Strait of Belle Isle being mixing areas of cod from adjacent divisions.