Asthma is a heterogeneous disease comprising several different phenotypes with probably different, but so far undefined causes and natural histories. Study designs based on longitudinal assessment of patients with different asthma phenotypes may improve understanding of their stability, natural history, persistence of disease and medication effectiveness. The aim of this study was to determine the frequency of different phenotypes depending on age group, the existence and types of allergic sensitisation and disease control in different phenotypes, linear growth and function of the adrenal gland at the beginning and at the end of the study in patients taking inhaled corticosteroids. This five year prospective study involved 201 patients with newly diagnosed asthma. PRACTALL guidelines were used to determine asthma phenotypes and disease control, treatment duration, the existence and types of allergic sensitisation in different phenotypes and age groups were monitored as well as height standard deviation score (SDS), ACTH and cortisol at the beginning and at the end of the study in patients taking inhaled corticosteroids. Application of certain clinical parameters enables phenotype classification for most patients and it remains stable in most of them, except in preschool children. Allergic asthma was the most prevalent phenotype in all age groups older than 3 years, house dust mite was the most prevalent allergen and good disease control was significantly more frequent in allergic asthma than in other phenotypes. Viral induced asthma was more prevalent in the younger age group, while exercise induced asthma was more frequent in the older age group. Allergic sensitization can be expected in all phenotypes. The disease was the most poorly controlled in the youngest age group. Inhaled corticosteroids, in recommended doses, have no effect on linear growth or adrenal gland function. Because of greater prevalence of some phenotypes in certain age groups, it is possible that age is a determinant factor for phenotype presentation. Contrary to previous research allergic asthma is the most prevalent phenotype already in preschool age group. High prevalence of allergic sensitisation in children aged 0-2 years and children with viral induced asthma requires monitoring of these patients because they do not represent sporadic viral wheeze. The optimal therapeutic strategy for wheezing disorders in early life remains unknown. Asthma is a chronic disease irrespective of phenotype.