Asthma in preschool children is greatly under-diagnosed worldwide. Aim was to investigate prevalence of wheezing, and asthma risk factors, doctor diagnosis, treatment and health resource utilization in preschool children. About 1402 children (3-5 years) attending local kindergartens participated in the study. The International Study of Asthma and Allergies in Childhood (ISAAC) written questionnaire (WQ) was used with additional questions on risk factors, asthma diagnosis, treatments, resource utilization. Allergic sensitisation was evaluated by skin prick tests for the common allergens. Prevalence of "wheezing in previous 12 months" and "doctor diagnosed asthma" were 12.1% and 8.6%, respectively. 4.7% of children have had both wheezing in the last 12 months and asthma diagnosis. Significant risk factors for wheezing were rhinitis, parental history of atopy and sensitivity to mites and grass pollens. 27.3% of children with asthma diagnosis, but only 4.9% of children without diagnosis, received regular treatment during the previous year (p<0.0001). Children with more than 4 episodes of wheezing a year received more frequently an asthma diagnosis, but 68.6% were not on regular treatment. Asthma diagnosis was associated with a significant increase in control visits for wheezing (p<0.0001). The prevalence of children requiring at least one hospital emergency visit in the previous year was not different among the two groups (83.3% vs. 82.5%). In preschool children the prevalence of wheezing and asthma is elevated. Preschool asthma seems to be under-treated with few cases receiving regular therapy. The social cost of the disease at this age seems to be elevated because of the high frequency of control and emergency visits.