The prevalence of asthma between birth and seven years was determined by questionnaire in 875 children as part of the Dunedin Multidisciplinary Child Development Study. From the combinations of asthma and/or wheezing reported in association with bronchitis, hayfever, eczema and allergies, a diagnosis of certain or probable asthma was made in 12.6 percent of these children. A further 22.6 percent admitted to wheezing, but a diagnosis of asthma could not be made with any certainty. Bronchitis was reported frequently, usually associated with wheezing. Children with more obvious asthma showed a male preponderance and significant differences in body build and school attendance compared with asymptomatic children.