Poultry production systems show variable production results despite standardization of both the genetic material and the birds' environment. Research on avian endocrinology has highlighted the influence of maternally derived yolk hormones on offspring phenotype. Artificial administration of corticosterone into eggs triggers behavioural and physiological changes in the chicks. However, the presence of elevated levels of corticosterone in bird eggs is disputed and egg injections may not result in physiological levels and distribution patterns. We artificially elevated plasma corticosterone concentrations in laying hens via subcutaneous implantation of corticosterone pellets (Ncorticosterone = 20, Nplacebo = 20). Hens were housed in outdoor aviaries (1,5x3m) in groups of four with one cockerel. Eggs were hatched or analysed for steroid hormone content. The presence of corticosterone was proven both in albumin and yolk in the eggs of the corticosterone implanted females via HPLC analyses. When compared to placebo-offspring (hierarchical models in MLwiN), the corticosterone implanted females' offspring grew slower the first 10 days of life (p = 0,015), they stole and ate less mealworms in a mealworm competition test (psteals mealworm = 0,001; peats mealworm = 0,023) on day 9, they were less right eyed lateralized (p = 0,011) on day 11. 11 weeks old they showed a lower antibody response to an immune challenge (p = 0,057), had higher baseline testosterone levels (corticosterone-offspring = 0,34±0,06 ng/ml, placebo-offspring = 0,1645±0,02 ng/ml; p = 0,022), and in adulthood performed shorter duration of tonic immobility (corticosterone-offspring = 75,80±11,49 sec., placebo-offspring = 180,37±12,50 sec.; p = 0,024). The results demonstrate that embryonic corticosterone exposure affects behaviour and physiology in chickens. Studying the effects of elevated prenatal hormone exposure in chicken may help to understand their behavioural ontogeny and explain the variability in behavioural problems in the poultry industry. The Dutch Animal Experiment Committee approved this experiment (project 5124A).