The hatchability of 205 incubation settings of eggs produced on 9 farms of Cobb broiler breeders was analyzed. For each farm, data from two successive flocks were analyzed. The age of the breeders for each flock varied from 28 to 60 weeks. The storage time of the eggs varied from 2 to 9 days under practical conditions (15 degrees C and 70% of relative humidity). The hatchabilities of the eggs from breeders of 28, 38 and/or 48 weeks of age and stored for 3 to 7 days were considered as the reference hatchabilities which characterize each flock. The age of the breeders, egg storage time, the reference hatchabilities and the setting season were fitted into a model that could be applied for the prediction of hatchability.