Prevalence of asthma and allergies in children shows large variations among different populations, but there is limited evidence about these conditions in immigrants from developing countries. The aim of this study was to evaluate the prevalence of asthma symptoms and allergies in immigrant children and adolescents living in Italy and to investigate the possible role of genetic and environmental factors in the development of such diseases. There were 1340 (4.0%) immigrants in Italy, mainly from East Europe (31.7%); 532 were born in Italy to foreign parents and 808 were born abroad. Asthma and other atopic diseases were on the whole significantly less common among immigrant children than among Italians, while some infectious diseases in the first two years of life resulted more present in immigrant children than in Italians.