Asthma morbidity increase every year, especially among children. The cause of this is multifactorial, but exposure to high levels of indoor allergens is thought to be one important factor, since we spend the large fraction (appx. 90%) of time indoors. Next to other popular indoor allergens (i.e. dust mites), many studies underline the importance of cockroach allergen. The purpose of this study was to evaluate the prevalence and importance of cockroach allergen in asthma among children in Łódź district. One hundred and sixty children, age 4-17, with bronchial asthma, were participated in this study. Each patient was examined, had skin prick test with common and cockroach allergens, measured total IgE level and undergone spirometry. Children with positive skin test to cockroach allergen had also measured specific IgE level to this antigen (immunoassay, CAP system). Our results showed that the most common allergen (by skin test), among these children, was dust mite 51.3%, followed by pollen 48.8% and cockroach allergen 24.3%. Among children with hypersensitivity to cockroach allergen 62% had also positive skin test with house dust mite and 59% with pollen. Average time of asthma duration in patients sensitive to cockroach antigen was 4 years and was similar to that of patients sensitive to dust mites and pollen. In children with cockroach sensitivity 13% had mild asthma, 26% moderate and 61% had severe asthma. We concluded that children with cockroach hypersensitivity have severe asthma more often than children with dust and pollen sensitivity. Class 3 and 4 in specific IgE levels correlated with severity of asthma. Our results showed that in children of Łódź distict, cockroach allergen is very important factor of sensitivity, next to dust mites and pollen. Hypersensitivity to cockroach antigen seems to influence the course and severity of asthma in children.