Fecundity estimates of Atlantic mackerel (Scomber scombrus) were derived from fish collected in 1987 off the coast of USA and Canada from two spawning contingents in the Northwest Atlantic. Estimates for females of 310 to 446 mm fork length in USA waters ranged from 155 900 to 1 643600 eggs. Fecundities for fish between 313 and 435 mm fork length in Canadian waters ranged from 208 500 to 1 548 400 eggs. The 5and 6-year-old fish were dominant in both locations. Fecundity was related to fork length, somatic weight and age in both spawning contingents. Fecundity estimates for the individual females in USA waters were lower than those in previously published results, while estimates for both the 1987 USA and Canadian contingents were higher than those reported previously for Canadian waters and a North Sea area.