Respiratory diseases with wheezing affect up to half of the preschool children population. These are not homogenous and include different phenotypes identified in the course of analysis of natural history of disease. This paper presents the original Martinez and coworkers' classification as well as its later modifications. About 40% of children with early wheezing suffer from asthma, however, asthma diagnosis is still being discussed especially in children below 5. Inflammation of airways in asthmatic patients has been proved in some studies, but up to date has not been used as diagnostics criterion. Relying on cohort birth studies asthma predictive index has been created. This includes clinical parameters and risk factors (especially related to atopy). However, final diagnosis requires exclusion of other causes of wheezing and positive response to therapeutic trial.