Different periods of hatching, called hatch windows, occur inside the same hatchery and birds' development could be affected by this. This study evaluated morphology of the intestinal mucosa and gizzard, and the presence of CD3+ cells in thymus, spleen, and intestinal mucosa in broiler chicks hatched from different egg weights and in different hatch windows. Eggs from breeders at 38 wk of age were evaluated in a factorial 3 x 2 experimental design, with 3 hatch windows (hatching before 472 h of incubation, between 472 and 488 h of incubation, and between 488 and 504 h of incubation) and 2 egg weights (lightweight and heavyweight). Prematurely hatched chicks remaining inside the hatchery for longer periods presented improved koilin membrane development in the gizzard, and smaller presence of CD3+ cells in thymus, spleen, and ileum compared with those birds that hatched close to the standardized time for hatchery opening.