Five experiments were conducted to determine the optimum day of incubation to stop turning eggs in high density plastic egg flats to obtain maximum hatchability. Eggs were set from Cobb broiler breeders with 511, 528, 525, 540, and 990 eggs/treatment in Experiments 1, 2, 3, 4, and 5, respectively, and from HyLine W-36 Leghorn breeders with 498, 540, 540, and 540 eggs/treatment in Experiments 1, 2, 3, and 4, respectively. Turning (once per hour) was stopped at incubation Days 13, 16, and 19 in all experiments and also at Day 10 in Experiments 1 and 2. Jamesway 252 incubators were used in Experiments 1 and 2; Robbins IH-A incubators were used in subsequent experiments.Hatchability of Leghorn eggs was significantly decreased by cessation of egg turning after 10 days but was not affected when turning was stopped at 13 days. Hatchability of broiler breeder eggs was not significantly affected by turning treatment in Experiments 1, 2, or 5 but was decreased following cessation of turning at Day 13 in Experiments 3 and 4. Embryonic mortality after 10 days of incubation occurred primarily in the last 4 days of incubation in both breeds. There were no differences between turning treatments in incidence of malposition. It is concluded that turning of hatching eggs can be stopped at 16 days of incubation without adversely affecting hatchability.